"Rubio and maybe Kasich," Greg Valliere, the chief political strategist at the Potomac Group said in an email.
"You get the sense, however, that Rubio is very well-positioned to gain strength. His favorable scores are excellent, he appeals to all wings of the party, and he's showing policy gravitas," Valliere added.
But he also is a candidate who, like Walker, appeals to both the establishment and more conservative wings of the Republican Party. And the expectation is that many of his donors — and perhaps some of his staff — will swing over to Rubio's campaign.
Erick Erickson, a conservative commentator and the editor-in-chief of RedState, told Business Insider in an email that he's heard most of Walker's donors seem to be favoring Rubio as an alternative — with Sen. Ted Cruz (R-Texas) and former Florida Gov. Jeb Bush (R) also in the mix.
"Rubio mostly," Erickson said in an email. "A few of his guys will go to Cruz. I know one who is looking at Jeb. But as I wrote this morning, I think we're going to see a Cruz v. Rubio primary and I think the way Walker donors are splitting proves it."
Photos of Marco Rubio on the campaign trail:
Marco Rubio on the campaign trail
Lots of people are saying Scott Walker's decision to drop out benefits one candidate in particular
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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Rubio looks stronger after impressing at the second Republican debate at the Ronald Reagan Presidential Library on Wednesday. A new CNN poll of Republican and Republican-leaning voters surveyed after the debate showed Rubio garnering 11% of the vote, up 8 points from a previous CNN poll earlier in September.
The surge put him in fourth place behind front-runner Donald Trump, former Hewlett-Packard CEO Carly Fiorina, and retired neurosurgeon Ben Carson. One top Walker donor told The Washington Post he donated to the campaigns of Rubio, Fiorina, Carson, and New Jersey Gov. Chris Christie (R) after the debate.
"I'm smart enough to know there could be big changes," media mogul Stanley Hubbard, the donor, told The Post on Monday before news of Walker's decision to drop out became public.
Several Republican campaigns already looked to gain supporters and donors like Hubbard from Walker's campaign on Monday.
Almost immediately after news broke of Walker's decision to drop out, Walker's co-chair in New Hampshire Cliff Hurst told the New Hampshire Union Leader that he would be supporting Sen. Marco Rubio (R-Florida). And according to BuzzFeed, Rubio's team was among four campaigns that had already reached out to former Nevada Gov. Bob List, Walker's Nevada campaign chair.
"Scott Walker is a good man who entered the presidential race after winning three grueling campaigns in four years," Rubio said in a statement on Walker's departure from the field.
"I know many people are disappointed with Scott's announcement and I respect what a difficult decision it must have been. He remains one of the best governors in the country and I have no doubt that he'll continue the fight for conservative principles."
Photos of Scott Walker on the campaign trail:
Scott Walker on the campaign trail
Lots of people are saying Scott Walker's decision to drop out benefits one candidate in particular
DES MOINES, IA - AUGUST 17: Republican presidential candidate and Wisconsin Gov. Scott Walker (L) holds a pork chop at the Iowa Pork Producers Pork Tent during the Iowa State Fair on August 17, 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)
Wisconsin Governor and Presidential candidate Scott Walker delivers keynote remarks at the DuPage County GOP Summer Reception Thursday, Aug. 13, 2015 at Carlucci's Restaurant in Downers Grove, Ill.(Anthony Souffle/Chicago Tribune/TNS via Getty Images)
WEST ALLIS, WI - AUGUST 12: Wisconsin Governor Scott Walker signs a bill approving financing for a new Milwaukee arena on August 12, 2015 at the Wisconsin State Fair in West Allis, Wisconsin. NOTE TO USER: User expressly acknowledges and agrees that, by downloading and or using this Photograph, user is consenting to the terms and conditions of the Getty Images License Agreement. Mandatory Copyright Notice: Copyright 2015 NBAE (Photo by Gary Dineen/NBAE via Getty Images)
CLEVELAND, OH - AUGUST 06: Republican presidential candidate Wisconsin Gov. Scott Walker fields a question during the first Republican presidential debate hosted by Fox News and Facebook at the Quicken Loans Arena on 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 political polls. (Photo by Scott Olson/Getty Images)
CHICAGO, IL - JULY 27: Republican presidential hopeful Wisconsin Governor Scott Walker washes down a 'cheezborger' with a Schlitz beer at the famed Billy Goat Tavern during a campaign stop on July 27, 2015 in Chicago, Illinois. Recent polls have Walker leading all Republican contenders in Iowa but trailing businessman Donald Trump and former Florida Governor Jeb Bush in New Hampshire. (Photo by Scott Olson/Getty Images)
Scott Walker, governor of Wisconsin and 2016 Republican presidential candidate, chats with staff as he leaves a campaign stop in Davenport, Iowa, U.S., on Friday, July 17, 2015. Wisconsins top court killed a criminal investigation of Walkers 2012 election campaign, removing a potential stumbling block to his presidential bid. Photographer: Daniel Acker/Bloomberg via Getty Images
Scott Walker, governor of Wisconsin and 2016 Republican presidential candidate, pauses during a campaign stop in Davenport, Iowa, U.S., on Friday, July 17, 2015. Wisconsins top court killed a criminal investigation of Walkers 2012 election campaign, removing a potential stumbling block to his presidential bid. Photographer: Daniel Acker/Bloomberg via Getty Images
DAVENPORT, IA - JULY 17: Republican presidential hopeful Wisconsin Governor Scott Walker steps off a motor home at a campaign event at Modern Woodman Park on July 17, 2015 in Davenport, California. Walker officially announced that he was seeking the Republican nomination for president earlier this week. (Photo by Scott Olson/Getty Images)
LAS VEGAS, NV - JULY 14: U.S. presidential candidate and Wisconsin Gov. Scott Walker speaks at Red Rock Harley-Davidson on July 14, 2015 in Las Vegas, Nevada. Walker launched his campaign on July 13, joining 14 other Republican candidates for the 2016 presidential race. (Photo by Ethan Miller/Getty Images)
Scott Walker, governor of Wisconsin, pauses during his presidential campaign announcement in Waukesha, Wisconsin, U.S., on Monday, July 13, 2015. Walker officially unveiled his White House campaign in the same venue where heÂ celebrated a June 2012 victory as the first U.S. governor to survive a recall election, after successfully confronting organized labor the previous year. Photographer: Luke Sharrett/Bloomberg via Getty Images
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Bush's campaign, meanwhile, announced on Monday that longtime Wisconsin GOP leader Richard Graber was backing the former Florida governor.
"Rubio and Carly. Rubio because donors and the political class have long viewed the two similarly — a new, conservative face of the national party with a good record who can appeal to every segment of the Republican voting block," one veteran Republican strategist told Business Insider.
"Carly may benefit because she's poised, based on her rise in the polls and continued over performance as a candidate, to enter into an important place in the primary — an outsider with substance. [I] suspect some Walker backers yearning for a true conservative alternative to other establishment candidates — Bush and Rubio — may give her a strong look."