The Republican establishment has finally fallen in love with Marco Rubio, but it may be too late.

With the specter of Donald Trump terrifying mainstream Republicans, Ted Cruz being Ted Cruz and Jeb Bush dropping out, lawmakers and party operatives are tripping over themselves to back the Florida senator's presidential bid.

During the past 72 hours, Rubio has racked up more than 20 endorsements from high-profile Republican leaders such as Bob Dole, Utah Sen. Orrin Hatch, North Carolina Sen. Thom Tillis and Arkansas Gov. Asa Hutchinson. Prominent megadonors like Joe Craft and political operatives including the Koch brothers' political guru Marc Short have also jumped on board.

The torrent of support follows months of calculated overtures from top Rubio operatives to Republicans on the sidelines and those supporting other candidates, with the senator making the case in public and private that he is the only Republican candidate who can unify the party and beat Hillary Clinton. 

The groundswell of support is being spurred by the increasingly urgent calls to stop Trump, a critical enough problem that mainstream Republicans are suddenly able to look past the fact that Rubio hasn’t won a single early primary contest and that he doesn't have a clear Super Tuesday victory in sight.

And it's unclear whether they'll move the needle for Rubio, whose support in the early primaries has been stuck in the low 20s. In fact, with the primary electorate in such an anti-establishment mood this year, the avalanche of endorsements from venerable politicians could actually bury Rubio, not his opponents, by making him appear as the new avatar of the Washington political class many voters so detest.

The endorsements are coming well after the bulk of the Republican Party's most-committed activists have already made up their minds. Trump continues to ride high in the polls — running more than 10 and sometimes 15 points ahead of the GOP field. The real estate magnate seemed poised as of Tuesday evening to best Cruz and Rubio again in Nevada, clinching what would be his third straight primary victory on the way to securing the Republican presidential nomination.

Also dampening the good news for Rubio: The biggest traditional advantage of support from lawmakers — help with fundraising and using elected officials' intricate knowledge of their home-state politics — is less because the two biggest primary days are just weeks away.

"You've got money, you've got a great candidate, you've got all the endorsements, you've got the right message — I don't know what more we can do except get 40 percent and get above Trump," said Rep. Tom Rooney (R-Fla.), one of Rubio's earliest congressional backers.

Rooney, who has traveled to Iowa, New Hampshire and South Carolina to stump for Rubio, said that he is continuing to work his colleagues. 

"I still have some work to do tonight in person with some of these guys that are still deciding," Rooney said. "A couple of my friends I knew were going to move over to Marco who aren't from Florida, and I told Marco's people certain people should be called directly by him."

But Rubio's operation said they've gotten a boost in momentum and fundraising as mainstream Republicans have fallen in line.

"We expect support to continue to surge," said one Rubio campaign aide. "All the people who don't want Donald Trump to be our next president know Marco is the only one who can beat him."

Rubio's surrogate program got a significant boost after the South Carolina primary. Bush's decision to drop out and Rubio's powerful speech — alongside South Carolina Gov. Nikki Haley, Sen. Tim Scott and Rep. Trey Gowdy — injected new life into the operation. Finance team members were huddled in a conference room at Rubio's headquarters in Washington, D.C., until 2 a.m. Sunday fielding calls from interested donors, according to a Rubio campaign aide.

The campaign isn't focused just on endorsements from household names. Rubio's campaign Monday also pointed reporters to a decision by a former Colorado lawmaker named B.J. Nikkel, a former co-chair of John Kasich's campaign in the state who decided after the South Carolina primary to throw her support behind the Florida senator. Although Nikkel isn't a household name outside of Colorado GOP circles, the rationale behind her decision aligns perfectly with the argument Rubio's campaign is making to donors who are considering Kasich.

Kasich, Nikkel said, "is a fine man and leader, but it's time for conservatives of conscience to rally behind the one man" who can defeat Trump.

Also in Colorado, Rubio's team picked up another key conservative leader on Monday, state Sen. Owen Hill, who had previously served as a state co-chair for Rand Paul and could help to turn out the Paul family's network of grass-roots activists, which has had an outsized influence on the GOP presidential caucuses there for the better part of a decade.

Colorado Sen. Cory Gardner was the first senator to back Rubio, back in November. Rubio's team has pointed to Gardner, who has regularly gone out on the campaign trail, as one of the next-generation politicians supporting his candidacy.

On Monday, four Florida Republican lawmakers jumped on with Rubio. Reps. Mario Diaz-Balart, Jeff Miller, Ileana Ros-Lehtinen and Carlos Curbelo put out a group statement throwing their political capital behind the only Florida Republican still in the race. The Florida delegation's growing support for Rubio could increase his chances of coming out on top in Flor ida's winner-take-all primary. Trump recently edged Rubio in polls in the state.

But the big prize, of course, is Jeb Bush, whose vast network of donors could help fuel Rubio's campaign as he squares off against a self-funded Trump and a well-stocked Cruz. Bush is slated to hold a national finance team call on Wednesday so that he can "personally thank" donors, according to an email sent by his team — marking a potential point of closure.

So far, however, many of Bush's Florida financial patrons have been slow to want to publicly throw their support behind Rubio. The slow pace of Bush financiers publicly moving to Rubio's team is in part a function of donors wanting to have some space after Bush's departure. Other loyal Bush supporters could stay on the sidelines for the rest of the 2016 cycle.

Rubio told reporters Tuesday that he and Bush spoke by phone and plan to meet in person sometime soon, but that he has yet to ask for his endorsement, which could serve as a symbolic blessing to his most loyal supporters that it’s OK to switch teams.

Outside of Florida, longtime Bush backers are less personally conflicted about moving their money to Rubio. But some of them aren't signing on right away, wanting instead to wait to better assess whether investing in Rubio might actually yield a dividend.

"We've got to catch our breath," said Fred Zeidman, a Houston banker and Republican Jewish Committee member who along with his son, Jay, actively worked to bundle contributions for Bush. "The goal is to beat the Democratic candidate in November, but we just need to step back and reassess which candidate has the best chance of doing that and then we'll move forward. But if I'm going to invest money, it has to pay off."

Although Zeidman said he's likely going to wait until after Super Tuesday to see where things stand before committing to Rubio or anyone else, he understands that time is running short for the GOP to unite behind one candidate who might be able to stop Trump from running away with the nomination.

"This whole thing could be over in two or three weeks," he said. "Time may be much shorter than people think."