A new poll set for release Monday shows former Florida Gov. Jeb Bush (R) lagging in a theoretical general-election matchup against Hillary Clinton, while Sen. Marco Rubio (R-Florida) is the only Republican candidate with a slight edge over the former secretary of state.
The new national poll from Public Policy Polling, shared exclusively with Business Insider, found Bush faring worse than any other major Republican candidate surveyed in a theoretical matchup with Clinton, the Democratic front-runner.
The PPP survey showed Clinton would lead Bush, 44% to 39%, in a theoretical general-election matchup, while 17% said they're still undecided.
Marco Rubio on the campaign trail:
Marco Rubio on the campaign trail
A surprising candidate would fare worst against Hillary Clinton in a general-election matchup
IN FLIGHT - FEBRUARY 10: Republican presidential candidate Sen. Marco Rubio (R-FL) talks with reporters on his charter flight from Manchester-Boston Regional Airport February 10, 2016 en route to Spartanburg, South Carolina. Rubio placed fifth in the New Hampshire primary, behind fellow GOP candidates Jeb Bush, John Kasich, Sen. Ted Cruz (R-TX) and Donald Trump, who swept away the competition with 35-percent of the vote. (Photo by Chip Somodevilla/Getty Images)
MT PLEASANT, SC - JANUARY 13: Republican presidential candidate Sen. Marco Rubio (R-FL) greets guests during a campaign rally at the Water Dog Grill on January 13, 2016 in Mount Pleasant, South Carolina. Tomorrow Rubio will join other candidates seeking the Republican nomination for president for a debate at the North Charleston Coliseum and Performing Arts Center in North Charleston, S.C.. (Photo by Scott Olson/Getty Images)
Senator Marco Rubio, a Republican from Florida and 2016 presidential candidate, waits to speak during a town hall meeting at the Maytag Innovation Center in Newton, Iowa, U.S., on Wednesday, Dec. 30, 2015. Rubio found himself under siege on two fronts Tuesday over his attendance record in the U.S. Senate as the Florida lawmaker embarked on a swing through snowy Iowa. Photographer: Scott Morgan/Bloomberg via Getty Images
MIAMI BEACH, FL - NOVEMBER 15: Republican presidential candidate Sen. Marco Rubio (R-FL) greets people before speaking during a community rally for 'Never Again' which was bringing attention to what the organizers say is a rise in worldwide anti-Semitism and the campaign against Israel's right to exist on November 15, 2015 in Miami Beach, Florida. Rubio continues to campaign for the Republican party's nomination. (Photo by Joe Raedle/Getty Images)
CEDAR RAPIDS, IA - NOVEMBER 21: Republican presidential candidate Sen. Marco Rubio (R-FL) speaks to guests during a town hall meeting on November 21, 2015 in Cedar Rapids, Iowa. Yesterday Rubio participated in the Presidential Family Forum in Des Moines with six of his Republican rivals for the nomination. Rubio has several campaign stops scheduled in the state today. (Photo by Scott Olson/Getty Images)
Republican presidential candidate Marco Rubio speaks at the Wall Street Journal CEO Council meetings in Washington, DC, November 16, 2015. AFP PHOTO / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)
ORLANDO, FL - NOVEMBER 12: Sen. Marco Rubio (R-FL) speaks at the Sunshine Summit opening dinner at Disney's Contemporary Resort on November 12, 2015 in Orlando, Florida.The dinner is the kick-off of a three-day event that will draw thousands of Republicans, mostly to hear live speeches from all the GOP presidential candidates on Friday and Saturday. (Photo by Tom Benitez - Pool/Getty Images)
ORLANDO, FL - NOVEMBER 13: Republican presidential candidate Sen. Marco Rubio (R-FL) speaks during the Sunshine Summit conference being held at the Rosen Shingle Creek on November 13, 2015 in Orlando, Florida. The summit brought Republican presidential candidates in front of the Republican voters. (Photo by Joe Raedle/Getty Images)
Senator Marco Rubio, a Republican from Florida and 2016 presidential candidate, speaks during a campaign rally at the Country Springs Hotel in Pewaukee, Wisconsin, U.S., on Monday, Nov. 9, 2015. Rubio will appear at Tuesday's Republican presidential debate in Milwaukee. Photographer: Daniel Acker/Bloomberg via Getty Images
CONCORD, NH - NOVEMBER 05: Republican Presidential candidate Marco Rubio (R-FL) files paperwork for the New Hampshire primary at the State House on November 5, 2015 in Concord, New Hampshire. Each candidate must file paperwork to be on the New Hampshire primary ballot, which will be held February 9, 2016. (Photo by Scott Eisen/Getty Images)
Republican Presidential hopeful Marco Rubio leaves the New Hampshire State House after filing for the state ballot November 5, 2015 in Concord, New Hampshire. AFP PHOTO/DON EMMERT (Photo credit should read DON EMMERT/AFP/Getty Images)
MANCHESTER, NH - NOVEMBER 4: Republican Presidential candidate Marco Rubio (R-FL) participates in a round table discussion at Saint Anselm College in Manchester, New Hampshire. Rubio is looking for a bump in the polls following a strong outing in the last debate. (Photo by Darren McCollester/Getty Images)
GREENVILLE, SC - SEPTEMBER 18: Sen. Marco Rubio (R-FL) speaks to voters at the Heritage Action Presidential Candidate Forum September 18, 2015 in Greenville, South Carolina. Eleven republican candidates each had twenty five minutes to talk to voters Friday at the Bons Secours Wellness arena in the upstate of South Carolina. (Photo by Sean Rayford/Getty Images)
NEW YORK, NY - OCTOBER 06: Republican presidential candidate, Sen. Marco Rubio (R-FL) speaks at Civic Hall about the 'sharing economy' on October 6, 2015 in New York City. Rubio, who has been experiencing a slight uptick in the polls after strong debate performances, has a second book out in paperback this Tuesday called American Dream: Restoring Economic Opportunity for Everyone. (Photo by Spencer Platt/Getty Images)
UNITED STATES - AUGUST 26: GOP Presidential candidate Sen. Marco Rubio, R-Fla., holds a town hall meeting in Londonderry, N.H., on Wednesday, Aug. 26, 2015. (Photo By Bill Clark/CQ Roll Call)
DES MOINES, IA - AUGUST 18: Republican presidential candidate and U.S. Sen. Marco Rubio (L) (R-FL) mans the grill with U.S. Rep. David Young (R) (R-IA) at the Iowa Pork Producers Pork Tent during the Iowa State Fair on August 18, 2015 in Des Moines, Iowa. Presidential candidates are addressing attendees at the Iowa State Fair on the Des Moines Register Presidential Soapbox stage and touring the fairgrounds. The State Fair runs through August 23. (Photo by Justin Sullivan/Getty Images)
UNITED STATES - August 17: Republican presidential candidate Sen. Marco Rubio, R-Fla., greets supporters during a Family Night event at Dean Park in Ankeny, Iowa, Monday, August 17, 2015. (Photo By Al Drago/CQ Roll Call)
NEW YORK, NY - AUGUST 14: Marco Rubio gives speach for the Foreign Policy Initiative at 3 West Club on August 14, 2015 in New York City. (Photo by Steve Sands/WireImage)
CLEVELAND, OH - AUGUST 06: Republican presidential candidate Sen. Marco Rubio (R-FL) participates in the first prime-time presidential debate hosted by FOX News and Facebook at the Quicken Loans Arena August 6, 2015 in Cleveland, Ohio. The top-ten GOP candidates were selected to participate in the debate based on their rank in an average of the five most recent national political polls. (Photo by Chip Somodevilla/Getty Images)
CLEVELAND, OH - AUGUST 05: Republican presidential candidate Sen. Marco Rubio (R-FL) greets guests gathered for a campaign event at Town Hall on August 5, 2015 in Cleveland, Ohio. Rubio is in Cleveland to participate in the Fox News GOP presidential candidate debate scheduled to take place tomorrow evening. The top ten polling Republican candidates were chosen to participate in the debate. (Photo by Scott Olson/Getty Images)
Senator Marco Rubio, a Republican from Florida and 2016 Republican presidential candidate, smiles while speaking during a rally at Town Hall restaurant ahead of the Fox News Republican Presidential Primary Debate in Cleveland, Ohio, U.S., on Wednesday, Aug. 5, 2015. Rubio will appear on stage with 9 other presidential candidates for the first Republican presidential debate tomorrow evening while former Texas Governor Rick Perry, former Pennsylvania Senator Rick Santorum, and Louisiana Governor Bobby Jindal didn't make the cut. Photographer: Andrew Harrer/Bloomberg via Getty Images
Senator Marco Rubio, a Republican from Florida and 2016 presidential candidate, speaks during the Faith and Freedom Coalition's 'Road to Majority' legislative luncheon in Washington, D.C., U.S., on Thursday, June 18, 2015. The annual Faith & Freedom Coalition Policy Conference gives top-tier presidential contenders as well as long shots a chance to compete for the large evangelical Christian base in the crowded Republican primary contest. Photographer: Andrew Harrer/Bloomberg via Getty Images
BOONE, IA - JUNE 06: Republican presidential hopeful U.S. Sen. Marco Rubio (R-FL) waits his turn to speak at a Roast and Ride event hosted by freshman Senator Joni Ernst (R-IA) on June 6, 2015 in Boone, Iowa. Ernst is hoping the event, which featured a motorcycle tour, a pig roast, and speeches from several 2016 presidential hopefuls, becomes an Iowa Republican tradition. (Photo by Scott Olson/Getty Images)
GREENVILLE, SC - MAY 09: Republican Presidential candidate U.S. Sen. Marco Rubio (R-FL) greets supporters at the Freedom Summit on May 9, 2015 in Greenville, South Carolina. Rubio joined eleven other potential candidates in addressing the event hosted by conservative group Citizens United. (Photo by Richard Ellis/Getty Images)
NASHUA, NH - APRIL 17: Republican presidential candidate Sen. Marco Rubio (R-FL) speaks at the First in the Nation Republican Leadership Summit April 17, 2015 in Nashua, New Hampshire. The Summit brought together local and national Republicans and was attended by all the Republicans candidates as well as those eyeing a run for the nomination. (Photo by Darren McCollester/Getty Images)
MIAMI, FL - APRIL 13: Republican Senator Marco Rubio of Florida makes a formal announcement that he is entering the 2016 Presidential race at the Freedom Tower on April 13, 2015 in Miami, Florida. (Photos by Charles Ommanney for the Washington Post)
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Sen. Ted Cruz (R-Texas) comes a bit closer against Clinton, garnering 43% support to Clinton's 45%, with 12% of voters undecided. Clinton ties retired neurosurgeon Ben Carson, 45% to 45%, while edging current Republican front-runner Donald Trump by a 46-43 margin.
Rubio, meanwhile, fared best among the candidates surveyed in the poll. He garnered 44% support to Clinton's 43%, with 13% of surveyed voters undecided.
The poll illustrates another obstacle for Bush, who once said the Republican nominee would have to "lose the primary to win the general" election. Despite his more moderate position on immigration relative to Trump or Cruz, the poll still found Bush performing — albeit within the margin of error — in the general election at this point.
What's dragging Bush down: He's the least-favorable Republican candidate in the field. Overall, just 24% of voters view Bush favorably, according to Public Policy Polling, while 53% see him in an unfavorable light. That's a worse net-favorability score than even Trump, who is viewed unfavorably by a 35-56 split.
Bush is attempting to regain some support among Republican primary voters by painting himself as a more "serious" candidate and sparring directly with Trump, putting foreign policy and national security front-and-center in his bid for the presidency.
A surprising candidate would fare worst against Hillary Clinton in a general-election matchup
BALTIMORE, MD - APRIL 10: Democratic presidential candidate Hillary Clinton holds a campaign rally at City Garage April 10, 2016 in Baltimore, Maryland. Voters will head to polling places for Maryland's presidential primary April 26. (Photo by Chip Somodevilla/Getty Images)
Democratic U.S. presidential candidate Hillary Clinton laughs as she listens to Representative Steve Israel (D-NY) speak on a gun control panel in Port Washington, New York April 11, 2016. REUTERS/Lucas Jackson
NEW YORK, NY - APRIL 09: Democratic presidential candidate Hillary Clinton holds a Latino organizing event on April 9, 2016 while campaigning in the Brooklyn Borough of New York City. The New York Democratic primary is scheduled for April 19th. (Photo by Andrew Renneisen/Getty Images)
SPRINGFIELD, MA - FEBRUARY 29: Democratic presidential candidate former Secretary of State Hillary Clinton speaks during a 'Get Out The Vote' rally at the Lyman & Merrie Wood Museum of Springfield History on February 29, 2016 in Springfield, Massachusetts. Hillary Clinton is campaigning in Massachusetts and Virginia ahead of Super Tuesday. (Photo by Justin Sullivan/Getty Images)
BOSTON, MA - Former Secretary of State Hillary Clinton speaks to supporters at the Old South Meeting Hall during a rally in Boston, Massachusetts on Monday February 29, 2016. (Photo by Melina Mara/The Washington Post via Getty Images)
MINNEAPOLIS, MN - MARCH 01: Democratic presidential candidate former Secretary of State Hillary Clinton greets patrons at Mapps Coffee on March 1, 2016 in Minneapolis, Minnesota. Hillary Clinton is campaigning in Minnesota as Super Tuesday voting takes place in 12 states. (Photo by Justin Sullivan/Getty Images)
MOUNT VERNON, IOWA - OCTOBER 7: Former Secretary of State Hillary Clinton speaks to voters during an outdoor town hall meeting at Cornell College in Mount Vernon, Iowa on Wednesday October 7, 2015. (Photo by Melina Mara/The Washington Post via Getty Images)
MUSCATINE, IOWA - OCTOBER 6: Former Secretary of State Hillary Clinton speaks to a voter before leaving a farm in Muscatine, Iowa on Tuesday October 6, 2015. (Photo by Melina Mara/The Washington Post via Getty Images)
MANCHESTER, NH - OCTOBER 05: Democratic presidential candidate Hillary Rodham Clinton holds a town hall meeting at the Manchester Community College on October 5, 2015 in Manchester, New Hampshire. Clinton spoke about the need for gun control on the wake of a mass shooting at another community college in Oregon. (Photo by Alfredo Sosa/The Christian Science Monitor via Getty Images)
DAVIE, FL - OCTOBER 02: Democratic presidential candidate Hillary Clinton speaks about gun control during her campaign stop at the Broward College Ã Hugh Adams Central Campus on October 2, 2015 in Davie, Florida. Hillary Clinton continues to campaign for the nomination of the Democratic Party as their presidential candidate. (Photo by Joe Raedle/Getty Images)
WASHINGTON, DC - SEPTEMBER 19: Hillary Clinton attends the Phoenix Awards Dinner at the 45th Annual Legislative Black Caucus Foundation Conference at Walter E. Washington Convention Center on September 19, 2015 in Washington, DC. (Photo by Earl Gibson III/Getty Images)
MANCHESTER, NH - SEPTEMBER 19: Democratic presidential candidate Hillary Clinton claps on stage during the New Hampshire Democratic Party Convention at the Verizon Wireless Center on September 19, 2015 in Manchester, New Hampshire. Challenger for the democratic vote Sen. Bernie Sanders (I-VT) has been gaining ground on Clinton in Iowa and New Hampshire. (Photo by Scott Eisen/Getty Images)
PORTLAND, ME - SEPTEMBER 18: Hillary Clinton brings her Democratic presidential campaign to Maine for the first time, speaking at King Middle School. Clinton is welcomed as she is introduced at the event. (Photo by Derek Davis/Portland Press Herald via Getty Images)
CEDAR RAPIDS, IA - SEPTEMBER 7: Democratic Presidential hopeful Hillary Clinton takes time to meet supporters and take photos at the Annual Hawkeye Labor Council AFL-CIO Labor Day picnic on September 7, 2015 at Hawkeye Downs in Cedar Rapids, Iowa. Clinton spent a busy Labor Day weekend in Iowa, meeting supporters throughout the state while trying to maintain a lead over Bernie Sanders for the Democratic nomination. (Photo by David Greedy/Getty Images)
US Democratic presidential candidate Hillary Clinton takes part in a discussion after speaking about the Iran nuclear deal at the Brookings Institution in Washington, DC, on September 9, 2015. Clinton expressed firm support for the nuclear accord with Iran, calling it flawed but still strong. Clinton added that the agreement must be strictly enforced and said that if elected president next year, she would not hesitate to use military force if Iran fails to live up to its word and tries to develop a bomb. AFP PHOTO/NICHOLAS KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images)
PORTSMOUTH, NH - SEPTEMBER 5: Democratic presidential candidate Hillary Clinton and U.S. Senator Jeanne Shaheen take an off the schedule stop in the River Run Bookstore before shaking hands with onlookers on September 5, 2015 in Portsmouth, New Hampshire. (Photos by Charles Ommanney/The Washington Post via Getty Images)
PORTSMOUTH, NH - SEPTEMBER 5: Democratic Presidential candidate Hillary Clinton receives an endorsement from U.S. Senator Jeanne Shaheen (D-NH) September 5, 2015 in Portsmouth, New Hampshire. Clinton attended a Women for Hillary event at Portsmouth High School. (Photo by Darren McCollester/Getty Images)
PORTSMOUTH, NH - SEPTEMBER 5: Democratic Presidential candidate Hillary Clinton walks downtown Portsmouth and takes pictures with people September 5, 2015 in Portsmouth, New Hampshire. Clinton attended a Women for Hillary event at Portsmouth High School earlier in the day and received an endorsement from U.S. Senator Jeanne Shaheen (D-NH). (Photo by Darren McCollester/Getty Images)
LAS VEGAS, NEVADA - AUGUST 18: Former Secretary of State Hillary Clinton answers questions from journalists after speaking to north Las Vegas voters at a town hall meeting in Las Vegas, on Tuesday, August 18, 2015. The former Secretary was answering questions about emails sent and received a private server system, now in question, while she was the Secretary of State. (Photo by Melina Mara/The Washington Post via Getty Images)
UNITED STATES - August 15: Democratic presidential candidate Hillary Rodham Clinton greets fairgoers as she tours the Iowa State Fair in Des Moines, Iowa, on Saturday, August 15, 2015. (Photo By Al Drago/CQ Roll Call)
CARROLL, IA - JULY 26: Democratic presidential hopeful and former Secretary of State Hillary Clinton speaks to guests gathered for a house party on July 26, 2015 in Carroll, Iowa. Although Clinton leads all other Democratic contenders, a recent poll had her trailing several of the Republican candidates in Iowa. (Photo by Scott Olson/Getty Images)
CHICAGO, IL - MAY 20: Democratic presidential hopeful and former Secretary of State Hillary Clinton arrives for a meeting with parents and child care workers at the Center for New Horizons on May 20, 2015 in Chicago, Illinois. Clinton arrived in Chicago after campaigning Monday and Tuesday in Iowa. (Photo by Scott Olson/Getty Images)
LAS VEGAS, NV - MAY 05: Democratic presidential candidate and former U.S. Secretary of State Hillary Clinton (C) poses with students and faculty after speaking at Rancho High School on May 5, 2015 in Las Vegas, Nevada. Clinton said that any immigration reform would need to include a path to 'full and equal citizenship.' (Photo by Ethan Miller/Getty Images)
NEW YORK, NY - APRIL 23: Hillary Rodham Clinton (L) and actress Maggie Gyllenhaal attend the 2015 DVF Awards at United Nations on April 23, 2015 in New York City. (Photo by Michael Stewart/FilmMagic)
NEW YORK, NY - APRIL 29: Democratic presidential hopeful and former Secretary of State Hillary Clinton speaks during the David N. Dinkins Leadership and Public Policy Forum at Columbia University April 29, 2015 in New York City. Clinton addressed the unrest in Baltimore, called for police body cameras and a reform to sentencing. (Photo by Kevin Hagen/Getty Images)
Hillary Clinton announced her campaign for president on Sunday April, 12, 2015 with a video on YouTube.
(Screenshot from YouTube)
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Indeed, since that time it appears that the opposite has occurred. He has seen his position sink in polls since mid-July, when polling averages found his support at above 17%. He's now in mid-single digits nationally. In the last month, however, his support rose slightly to 7% compared to the previous month's PPP survey.
Publicly, many in Bush's orbit say they are completely unconcerned by former governor's stagnating poll numbers.
"The race is immaterial. They're starting to figure out — who do I want to be president, and who do I want to see in the Oval Office? Who do I want to be commander in chief?" former Department of Homeland Security Secretary Tom Ridge told Business Insider earlier this month. "So that's why I think he's gaining momentum. I don't care what the polls say. I've never been a big believer in national polls."
But privately, some prominent Republicans who had expressed support for Bush have cast doubt on his comeback chances.
"The race is turning into a three man contest — Trump (outsider lane), Cruz (conservative lane), Rubio (establishment lane) with [New Jersey Gov. Chris] Christie trying to dislodge Rubio in the establishment lane with a win" in New Hampshire, a former senior adviser to 2012 Republican nominee Mitt Romney told Business Insider last week.
Beyond the Republican race, Monday's poll also showed the potential weaknesses of Sen. Bernie Sanders (I-Vermont) in the Democratic field.
Despite his impressive grassroots fundraising hauls and the massive crowds that attend his rallies, it's still no surprise that Clinton has touted her chances in a general election. She fares slightly better in several head-to-head matchups with top-tier Republican candidates like Bush, Cruz, Trump, and Rubio.