The fate of an immigration overhaul rests almost exclusively with Sen. Marco Rubio, the Florida Republican whose star power with conservatives is crucial to moving a bill through Congress.

President Barack Obama retains veto power, and Democrats hold the Senate floor. But no comprehensive immigration changes are likely to pass Congress without the healthy support of House Republicans. And Florida’s junior senator, perhaps more than any other Republican serving in Washington today, has the political credibility and communication skills to sell such complicated, sensitive legislation to skeptical conservative members, grass-roots voters and influential media commentators.

Rubio’s position is all the more unique because congressional Democrats and Obama need him, too, and appear to realize his importance to the legislative endgame.

Republicans warn that Obama and congressional Democrats could sink Washington’s immigration policy rewrite by attaching controversial social provisions or watering down the border enforcement and security measures included in the bipartisan Senate framework that Rubio helped negotiate. The Florida lawmaker has said he’ll pull his support from any bill if that occurs, and Republicans say comprehensive policy changes will fail to garner meaningful GOP support without Rubio’s backing.

“If Rubio signals any mistrust or misgivings, the whole thing collapses,” GOP pollster Brock McCleary said.

Rubio, 41, was elected to the Senate only two years ago, yet he finds himself not just leading the debate on one of the most politically contentious issues Congress faces, but possibly being the central figure. Republicans on Capitol Hill give him all the credit for the fact that policy changes are a possibility at all.

Rubio’s push for an immigration overhaul has broad implications for the future of the Republican Party, which fared extremely poorly with minority voters in 2012 and is looking to rebound in the 2014 midterm elections and the 2016 presidential race, in which the senator is considered a leading GOP contender. But Republicans familiar with Rubio’s thinking say his desire to reform U.S. immigration law is rooted in his experience as a member of a south Florida community of Cuban immigrants and exiles.

Still, the politics are not lost on Rubio, nor is his particular significance to the outcome of Washington’s latest effort at wholesale immigration changes.

“He understands he has the kind of credibility with the conservative base that will be needed to help sell this to them. He also understands that if he walks away because the deal they reached changes, the bill will lose significant potential conservative support,” a GOP strategist said.

Grass-roots conservatives and Republican lawmakers opposed to a comprehensive immigration overhaul worry that the final bill would legalize the status of about 11 million illegal immigrants already in the country without ensuring that border security provisions are implemented. That deep skepticism is driven by what happened in 1986, when President Ronald Reagan agreed to amnesty for 3 million undocumented immigrants on the promise of border security improvements that never materialized.

Rubio’s considerable challenge is to sway wary conservatives — on Capitol Hill, around the country and in the media — who feel burned by what happened under Reagan.

A Democratic Senate aide to a member of the group of eight senators behind the bipartisan framework said Rubio has impressed Democrats by being fearless in selling policy changes “to the most conservative corners of his party.” But in fact, Rubio has influence because he comes directly from the GOP’s conservative wing.

Perhaps just as important, Republican strategists say, is that the Floridian has a well-planned communications strategy designed to reach conservatives where they get their news and to appeal to their sensibilities. Rubio, they say, is effective both because he has submitted himself for interviews with every major conservative talk radio host in America and because he speaks their language. Few Republicans with Rubio’s crossover appeal are capable of this feat.

“Sen. Rubio has built a framework of legislative principles, but he also built a communications plan around his push for reform,” a GOP strategist and former congressional aide said. “Could anyone else have gone on Rush Limbaugh and performed the way he did and made the case for immigration reform the way he did? I don’t think so.”

The fact that there hasn’t been an all-out groundswell in opposition to the plan appears to stem from Rubio’s central involvement. But widespread skepticism remains, and with a potential primary challenge in the back of their minds, members will likely be cautious about supporting anything that might be deemed “amnesty.”

Rubio appeared on several conservative talk radio shows Tuesday and Wednesday as part of a campaign to explain why the plan should be palatable to conservatives. Despite his doubts about Obama’s motives and intentions, Limbaugh called Rubio’s efforts “admirable and noteworthy.”

However, the road ahead is rough, with or without him.

Republican lawmakers who are already against the plan have taken to the Senate floor and to the airwaves to voice their concerns about enforcement.

On Laura Ingraham’s show Wednesday, Sen. David Vitter, R-La., called Rubio “amazingly naive” to think that enforcement will materialize. A day earlier on the same show, Rep. Lamar Smith, R-Texas, an original Tea Party Caucus member and a significant voice on immigration within the conference, called the plan “mass amnesty” and referred to the House as a potential “firewall” for the bill.