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Marco Rubio is scoring some big endorsements. But do they matter?

Rubio has occupied an odd place in the GOP race all year: Never the front-runner, but always — in theory — on the verge of breaking out.

Sen. Marco Rubio has occupied an odd place in the GOP race all year: Never the front-runner, but always — in theory, on paper, hypothetically — on the verge of breaking out. 

On Tuesday, Rubio once again showed signs of imminent liftoff after snagging one of the biggest endorsements in the race so far in Rep. Trey Gowdy of South Carolina. 

Gowdy, the high-profile chair of the House Select Committee on Benghazi, is the increasingly rare politician who’s popular in both conservative and establishment circles. He easily could have succeeded John Boehner as House speaker had he chose to run. 

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“National security, public safety are the most important issues to me and there is nobody better on those two issues than Marco Rubio,” Gowdy told a crowd in Iowa alongside the candidate. 

Rubio has spent all year waiting for Republican leaders like Gowdy to coalesce around him. His unflashy campaign operates under the assumption that as other establishment-friendly options like Jeb Bush fade away, Rubio will become the natural destination for the politicians, donors, commentators, and activists who have helped choose the past several nominees. His polling may look unspectacular now, but once that party consensus finally clicks into place, he should have more than enough juice to overcome insurgents like Sen. Ted Cruz and Donald Trump.

Rubio has good reason to think his plan might work. The most prominent political science theory today is that party elites tend to pick the eventual nominee over the course of an “invisible primary” that takes place in the months and years before voters head to the polls, at which point rank-and-file partisans usually fall in line behind their choice.

The idea was popularized in "The Party Decides: Presidential Nominations Before And After Reform," an influential 2008 book by researchers Marty Cohen, David Karol, Hans Noel, and John Zaller. Political nerds have cited it routinely throughout the race. Nate Silver may be famous for analyzing general election polling, but when it comes to primaries FiveThirtyEight has consistently urged readers to put their faith in endorsements, which he tracks on the site, over surveys. 

So how’s Rubio been doing on that front? Sure enough, he’s made gains as rivals like Bush and Scott Walker have fallen. Bush took an early lead in endorsements from top donors and federal lawmakers that he still holds, but Rubio has racked up more support from both in the last three months than anyone else in the race. Among the big names: Rising stars Cory Gardner and Steve Daines in the Senate, well-known figures like Kristi Noem, Darrell Issa, and Mia Love in the House, and major party funders like billionaire Paul Singer. 

All this is good news for Rubio, who surely has more names ready to roll out before voting begins, but it’s still a long way off from a tipping point. And his gains in elite support have yet to translate into much change in polls, where he’s stalled at around 11 percent to 13 percent support in surveys of GOP voters nationally and in Iowa and New Hampshire.

“I don’t think anyone is winning the invisible primary,” Georgetown professor Hans Noel, co-author of "The Party Decides," told MSNBC in an e-mail on Tuesday.

In some ways, Rubio has lost ground. New Jersey Gov. Chris Christie — who could also theoretically command establishment support — has sprung to life in New Hampshire. Meanwhile, Bush may be wounded, but he’s competitive enough in the same state to justify continuing his campaign. His well-funded supporters at Right to Rise PAC launched a new round of negative ads targeting Rubio this week. 

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Rubio doesn’t have any unique advantage in Iowa, which Cruz looks favored to win, or New Hampshire and South Carolina. If he doesn’t dominate the establishment lane in the first few contests, he might never get off the ground.

Who’s to blame for Rubio’s ongoing failure to launch? Noel points the finger at the candidate currently leading national polls who seems to short circuit every theory of conventional politics. 

“Trump seemed to suck all the air out of the process, and that made it hard for people to figure out which of the party-friendly candidates (Bush, Rubio, Walker, Christie, etc.) were the best,” Noel said. “So Trump had an impact, even if he’s not the nominee.” 

This failure to cohere has created an opening for an unconventional candidate like Trump or Cruz to potentially break out of the usual “party decides” model. 

Cruz has worked hard to win over social conservative leaders via traditional means, especially in Iowa, but Noel views him as a “factional” candidate based on his present support — typically not the type who can grab the nomination. In Trump’s case, he’d break the mold entirely. 

“Trump doesn’t fit the 'Party Decides' story,” Noel said. “The party doesn’t want him.”

Noel is skeptical of Trump’s chances, but if there’s one thing driving his campaign, it’s the waning influence of the exact kinds of party leaders and activists who Rubio is counting on to drag him past the finish line.

“The biggest explanation for Trump is the lack of trust that many have of the party,” Noel said. “This seems to be the defining characteristic of the Tea Party — they like the policies that the Republican Party says it is for, but they don’t trust Republicans to really push for those policies. They also don’t trust the party to manage the Republican coalition to the benefit of those goals.”

Rubio’s new backer Gowdy understands this dynamic as well as anyone. After Boehner was hounded into resigning by an ultra-conservative insurgency, some Republicans called on Gowdy to take over in order to unite the party. The reason Gowdy gave for turning them down was instructive: No one can unite the party, because whoever tries will inevitably be labeled a sellout on the right.

“I think the House is bordering on ungovernable right now,” Gowdy told NBC in October. 

Trump responded to news of Gowdy’s endorsement in the usual way this week, declaring on Twitter that the congressman “failed miserably” questioning Hillary Clinton at the Benghazi Committee and retweeting a supporter who called him a “Benghazi loser.” Two months ago, Trump’s campaign spokeswoman Katrina Pierson led an online campaign to draft Gowdy as speaker.