Will Marco Rubio save immigration reform — or kill it?

Sen. Marco Rubio (R-Fla.) cemented his role Sunday as the leading face of immigration reform when the first-term senator appeared on seven Sunday news shows, forcefully promoting a bipartisan bill ahead of its scheduled unveiling later this week.

Though Rubio is just one of the so-called Gang of Eight senators who have been working on the compromise deal, he's been by far its most visible member. With full details of the bill expected to come out this week, his role going forward will be crucial to the legislation's success — or its failure.

"After offering lukewarm support until now, Rubio is preparing to fully embrace a measure that is the most significant of his political career so far," says Politico's Manu Raju. "The gambit could pay off in spades by crowning a leading presidential contender in 2016, or it could permanently damage the Republican's brand with conservatives."

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Rubio's presence has been instrumental in building Republican support for the legislation, and it will be crucial in determining the bill's ultimate fate. His GOP star power has made the normally contentious issue less so for other would-be deal-makers in the party; Sen. Lindsay Graham (R-S.C.), another member of the bipartisan immigration group, hailed Rubio as "indispensable" to their efforts.

"Without Rubio, Obama and the Democrats wouldn't have nearly as many Republicans who appear to be willing to be part of an immigration bill that has the president's support," says the Washington Post's Ed Rogers. "And without Rubio, the other Republican leaders on immigration — Sens. Lindsey Graham (R-S.C.) and John McCain (R-Ariz.) — would not have the same level of deference among Republican leaders on this issue as they do now."

As the party's point man on immigration, Rubio will be central to assuaging conservative concerns — especially now that's he's gone all in on the measure. One of the most common gripes about the bill is a fear that it would give undocumented workers amnesty in tandem with a pathway to citizenship. Both of those terms have been politically perilous for Republicans who have waded into the immigration debate in the past.

Fears of amnesty helped sink President George. W. Bush's attempt at a major immigration overhaul. And both Jeb Bush and Sen. Rand Paul (R-Ky.) have tripped over the issue this year, with Paul having to walk back his remarks to clarify that he endorsed legal status for undocumented immigrants, but not through a new pathway to citizenship.

Already, Rubio has had to tamp down concerns among those in his party. On Sunday, he repeatedly said the bill was not tantamount to amnesty, noting that it would send undocumented workers through the existing legal immigration process with some additional restrictions, while also implementing new border security benchmarks.

"It doesn't reward or doesn't award them anything," Rubio said. "But it does give them access to our legal immigration system through a process that will not encourage people to come here illegally in the future, and then through a process that isn't unfair for people that have done it the right way."

Rubio is reportedly also pitching the bill to conservative thought leaders, like the editors of the Weekly Standard, hoping to ease anxiety from that corner. And on Monday, the Senate bowed to mounting concern about the bill advancing too quickly, moving back a scheduled hearing on the legislation to give lawmakers more time to read it.

Until last weekend, there was some doubt as to whether Rubio would jump ship on his own bill. But now that he's taking such great pains to push the deal toward completion, some say the odds of a final bill passing the Senate have gone up dramatically.

"So long as Rubio was looking for a way out, stakeholders planned for the possibility that the bipartisan process [would] stumble badly, and the only 'Gang of Eight' member likely to seek national office would walk away, undermining the plan," says MSNBC's Steve Benen. "But with Rubio taking the plunge, finally taking on a leadership role, reform proponents have reason for optimism."

Still, Rubio could wind up on the other side of the bill as it maneuvers through the Senate.

He's acknowledged that he could break with the Gang of Eight over amendments added to the legislation. And though he's said the bill is only a "starting point," that could be revised, he's also said he may walk away if it changes too much. Rubio has a fine line to walk on the issue, and if he sees a final bill as too lenient for conservatives to swallow, he could bow out to avoid their ire.

"He could always argue that Obama was too squishy on enforcement, or too union-friendly on guest workers, or whatever; he'd be a hero to the base for standing up to the sharia socialist, and he could still get some mainstream-media credit for supporting reform as long as he did," says TIME's Michael Grunwald.

Rubio is widely expected to be plotting a 2016 White House bid, and irking the party base would make that goal a lot harder. Should he ultimately jump ship, the bill's prospects of becoming law would likely go down with him.

"It's no exaggeration to say that if Rubio walks away from the final product on immigration, the bill might not make it," says the Washington Post's Chris Cillizza.