On Thursday, a bipartisan group of senators unveiled the framework for a broad immigration overhaul, setting the stage for Congress' next big legislative fight.

In formally announcing the bill, the Gang of Eight — four Democrats and four Republicans — vowed that their legislation would not see the same fate as gun control efforts, which collapsed Wednesday in the face of a series of Republican filibusters. Yet stiff opposition to the immigration reform bill remains over concerns that it would forgive undocumented workers who entered the country illegally, raising the question of whether this major legislative effort will also wind up on the Senate scrap heap.

"I think the majority of people in both caucuses really want to get this done," Sen. Chuck Schumer (D-N.Y.), one of bill's authors, said Thursday. "I believe this is ours to lose."

"I don't think that it's at all like gun control, frankly," he added, blaming "powerful outside forces" for scuttling that effort.

Indeed, the immigration bill has gained the backing of a motley array of partners, from big business and labor groups to fiscal conservatives and immigration activists. At Thursday's press conference, both AFL-CIO head Richard Trumka and anti-tax crusader Grover Norquist stood with the Gang of Eight, highlighting the bill's diverse crowd of backers. Supporters hope a broad coalition will ensure that immigration reform doesn't fall victim to the partisan gridlock that has dominated Washington in recent years.

The bill would provide a path to citizenship for the estimated 11 million undocumented workers in the country. In exchange, it would tighten border security, a provision seen as crucial to attracting immigration hawks who've said border security must be a prerequisite to a broader immigration overhaul.

While still a divisive issue, immigration reform is less politically perilous for the GOP than gun control, says ABC's Ted Hesson, noting that Republicans are starting to view reform as something of an electoral necessity. The Republican Party candidly acknowledged earlier this year that it could no longer afford to lose so much of the Hispanic vote to Democrats, and some see immigration reform as one way to appeal to those voters.

That's a point Sen. John McCain (R-Ariz.) conceded in Thursday's press conference.

"Republicans have got to compete for the Hispanic vote," he said. "Passage [of this bill] does not gain a single voter, but it does put us on a level. Right now we are not competitive because this issue has got to be resolved."

Crucial to the Gang of Eight's success is Sen. Marco Rubio (R-Fla.), who has made himself the face of the reform effort. A Tea Party freshman widely believed to harbor presidential ambitions, Rubio, with his GOP star power, has long been seen as vital to providing cover for, and thus winning over, skeptical conservatives.

However, in a series of interviews with conservative talk radio hosts over the past two days, Rubio has struggled to sell the bill. Talk radio was credited with helping to defeat a proposed immigration overhaul in 2007, and Rubio had hoped to give his legislation a big boost by winning that crowd over. Yet in his recent interviews, hosts remained skeptical of the bill, with some saying flatly they'd never support it.

"The limits of Marco Rubio's persuasive powers and charm, and the depth of conservative reservations about immigration reform, are beginning to show themselves," says the Huffington Post's Jon Ward of the tepidly received media blitz.

Conservative critics have brandished the dreaded A word — amnesty — to rally opposition. A group of conservative senators held their own press conference Thursday to denounce the bill, with Sen. David Vitter (R-La.) blasting it as a recipe for "immediate amnesty."

Some Republicans have also quietly floated the possibility of killing the bill with a poison pill amendment — an egregious amendment tacked on to legislation to make the full bill too unpopular to pass. Other senators have raised concerns about the possible price tag of the legislation, citing that as a reason why it should not pass.

One possible sticking point to watch in the coming days: Hawks have demanded that any pathway to citizenship be triggered only when tighter border controls have been implemented. The Gang of Eight has included such triggers, but the requirements are somewhat vague. For all practical purposes, "there's still no way to know how the bill's benchmark border security stats will be determined," says Ian Gordon at Mother Jones. And that may be another reason for conservatives to kill the bill.

We'll have a better idea of where senators stand when the 844-page bill has its first hearing Friday. It's expected to come up for a vote before the full Senate sometime in June.