When he suspended his campaign, Marco Rubio said he wasn't running for president but urged local GOP officials to let him keep his delegates.
A month later, Rubio is still third in the Republican hunt, ahead of John Kasich, with an impressive 10 percent of all delegates awarded so far. It's a potentially pivotal margin for an open convention.
It turns out, however, that Rubio won't get to keep them all.
The Florida senator's strategy is hitting some turbulence, NBC News has learned, because several state parties have determined Rubio does not get to hold onto all his delegates.
Only 34 of the 172 delegates Rubio won in the primaries will be immediately up for grabs on the first ballot in Cleveland. That development is opening up a fierce competition to win these lapsed Rubio delegates, which are located in Oklahoma, Minnesota and Louisiana.
"Our state rules say if someone is not on the ballot, they are free to vote for whomever they choose," said Oklahoma GOP chair Pam Pollard, "and I support that."
"We have 12 bound delegates for Rubio," she told NBC News, "so if he is not on the ballot — those 12 delegates are free to vote whatever way they want."
Delegates are liberated to switch teams, under Oklahoma law, when their candidate "is for any reason no longer a candidate."
Minnesota, where Rubio won his second largest haul with 17 delegates, applies a similar rule. The state party ruled that delegates may "vote for any candidate" if the one they support is not on the first ballot at the convention.
The icing on the cake for Rubio's rivals is that most of his lapsed delegates have not even been selected yet, making them easier to pick off.
RELATED: Marco Rubio on the campaign trail:
Marco Rubio on the campaign trail
Lapsed Rubio delegates are up for grabs on convention's first ballot
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)
While Donald Trump is blasting the delegate system on the campaign trail, including criticizing the RNC for allocations made mostly by state parties, MSNBC has learned the Cruz campaign is continuing a laser focus on picking up delegates.
Cruz supporters are currently running for Rubio spots in Minnesota, and last weekend, Cruz won new delegates at local conventions in Oklahoma. During that effort, the Texas senator's allies filled a Rubio slot with Robert Carter, a minister from Grove, Oklahoma who backs Cruz.
Carter said if the GOP advises him the rules allow it, "I will pledge a vote for Cruz on the first ballot," and the senator's aides tell MSNBC they are finding a warm reception at the grassroots level.
"We are pleased at the response that the Rubio contingents at state conventions and congressional delegate selection events are showing our campaign," a senior Cruz adviser said.
Another Republican source close to the Cruz campaign said the team has been laying ground work to grow their delegate support from "day one." Now, they are organizing to fill Rubio slots or win over Rubio backers, arguing, "Ted could move the country more in the direction Marco wanted to go than Trump wants to go," the source told NBC News.
The lapsed Rubio delegates are especially crucial for Trump, based on his best path to the nomination, as they are part of a small pool of unbound delegates that, unlike most, are totally up for grabs on the first ballot.
If Trump finishes the primaries fairly close to the 1,237 majority, he would only need a few of those delegates to put him over the top. (Everything changes on subsequent ballots, when all delegates are unbound from their candidate preference.) So Trump's best bet is to win on the first ballot, when all his delegates are required to support him under the rules. A few of the extra unbound delegates could close the deal in that instance.
The Cruz Campaign has been steadily blunting that option for Trump, however, by gobbling up the bulk of unbound delegates to date. Cruz excelled at recent conventions in Colorado and North Dakota, which make up 45 percent of all the unbound delegates under state rules. (The other unbound delegates remain in places like Pennsylvania and Guam.)
If Cruz also locks down most of the 34 lapsed Rubio delegates, there will be very few left for Trump to woo if he doesn't achieve a majority in the remaining primaries.
The maneuvering reveals Cruz's two-step strategy for a convention: first, denying Trump the nomination on the first ballot by blocking him from unbound delegates; then consolidating the anti-Trump vote on later ballots.
RELATED: 10 Facts About Marco Rubio:
10 facts about Marco Rubio
Lapsed Rubio delegates are up for grabs on convention's first ballot
1. His parents, Mario and Oria, are Cuban immigrants.
(Photo by Joe Raedle/Getty Images)
2. Attended Tarkio College for one year on a football scholarship before he later transferred to Santa Fe College.
3. When he was sworn into office in 2011, he said that he owed $100,000 of student loans which he finally paid off in 2012.
(Mary F. Calvert/MCT via Getty Images)
4. His wife of 17 years, Jeanette, is of Colombian descent and was once a Miami Dolphins cheerleader.
(Photo by Joe Raedle/Getty Images)
5. He went viral with a sip of water. Rubio gave the official Republican reaction to the State of the Union in 2013, but the only detail most people remembered was the moment in which he became so parched that he reached for a water bottle to quench his thirst.
(Photo by Brooks Kraft LLC/Corbis via Getty Images)
6. Though he was baptized as an infant in the Catholic church, he was also baptized as Mormon later in childhood when his family lived in Las Vegas. He is now a practicing Catholic.
(Photo By Tom Williams/CQ Roll Call)
7. He teaches political science at Florida International University in Miami.
(Photo by Charles Ommanney for the Washington Post via Getty)
8. He says the first concert he ever attended was a Prince show.
(Photo By Tom Williams/CQ Roll Call via Getty)
9. His family used to call him Tony, which came from his middle name Antonio.
(Photo by Joe Raedle/Getty Images)
10. He was speaker of the Florida House before he was a U.S. Senator.
(Photo by Joe Raedle/Getty Images)
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It is the political equivalent of Owen Wilson's plea in the final scene of the 2005 film "Wedding Crashers." Wilson's character barges into a wedding, quiets the room, and tells his crush, "I'm not standing here asking you to marry me — I'm just asking you not to marry him!"
Cruz is not playing to win on the first ballot, he's asking the delegates to hold off on Trump.
Frank Donatelli, a Republican operative who worked for Reagan at the 1976 contested convention, says the strategy makes sense because "if Trump doesn't win on the first ballot, he's in trouble."
"If Trump is short and has to go into the uncommitted pool, these are the people you have to appeal to," he told MSNBC.
Donatelli, who endorsed Rubio, says the senator could have influence at the convention because of his delegates.
"I want to make sure that they're there on the first ballot," Rubio told conservative radio host Mark Levin on Tuesday.
Rubio did not suggest he had much sway over them on subsequent balloting, noting that after the first ballot, delegates "will be free to vote for another candidate, and I hope that they'll nominate a conservative."
According to the MSNBC tally, Rubio's remaining 138 delegates will be unbound on the subsequent ballots, and local GOP officials have the same expectation.
In Georgia, where state law binds delegates on the first ballot unless a candidate completely "withdraws," Party Chairman John Padget echoed Rubio's analysis.
"He has the delegates for the first ballot at the convention," Padget said, "and then my delegation can vote whatever way they want on a second ballot."
Tennessee GOP chairman Ryan Haynes made a similar point.
"Our delegates will be bound for two rounds," Haynes said, "even if his campaign is suspended." The requirement is in a state law.
"In Virginia, all 16 delegates are bound on the first ballot, no matter the status of his campaign," Virginia GOP spokesman David D'Onofrio told NBC News. "Even if he stood up and said, 'All of my people should vote for x,' in Virginia, they are bound to him on the first ballot."
During that convention discussion, D'Onofrio also echoed a theme from his national GOP counterparts, who have been exasperated as Trump has blamed party rules for his own campaign's stumbles.
"We've got plenty of rules, but they've been known for a long time," D'Onofrio said, adding, "it's incumbent on everyone to know what the rules are."