Senate Republicans involved in touchy negotiations to overhaul immigration laws reaffirmed their commitment Tuesday to establishing a path to citizenship for those now living in the United States illegally--despite a surprising defection on the key issue from former Florida Gov. Jeb Bush.

But two key members of that group acknowledged for the first time Tuesday that they may not have a bill ready to introduce until April, after Congress’s two-week Easter recess. The eight-member group had been aiming to advance a bill in March.

Bush, a longtime proponent of immigration changes, surprised many immigrant advocates this week with the publication of a long-awaited book on the topic. In the book, he advocates allowing the nation’s 11 million illegal immigrants to seek permanent legal residency in the United States, but not citizenship.

That issue has already shaped up to be one of the key dividing lines in the Congressional debate over immigration. Illustrating the shifting ground, Bush has given several interviews as part of the book roll-out further revising his position and indicating that he could, in fact, support a path to citizenship.

In a statement of principles published in January, the eight-member Senate group endorsed a path to citizenship, but a number of House Republicans have objected.

Sen. Lindsey Graham (R-S.C.), a member of the group, said he was “surprised” by Bush’s proposal, particularly since it comes from a governor who had long been out front on the need for an immigration overhaul and is well-liked in the Hispanic community.

He argued members of the Republican party who believe it is amnesty to allow illegal immigrants to remain in the country will not be appeased by denying them eventual citizenship.

“From a policy point of view, I don’t think it’s the right approach. I don’t like the idea of having millions of people here for their entire life without being able to assimilate into America,” he said. “From a political point of view, we’ve got 55 Democrats sent and a 72 percent support for a path to citizenship. It’s just not practical to think we’ll be able to pass any bill in the United States Senate without a path to citizenship.”

Behind the scenes, advocates and congressional sources familiar with the negotiations say the path to citizenship is not the trickiest issue facing the Senate group, which has been working to translate a joint statement of principles into a bill since January,

They say the more difficult issue for the Senate group has been how to structure a low-skill visa for temporary workers, an issue that has helped stymie past efforts to rewrite immigration laws.

Though the group has been meeting two to three times a week, it has not yet been able to resolve the difficult topic.

AFL-CIO President Richard Trumka came to the Hill on Tuesday to meet with the gang’s four Democratic members, as the two sides shuttle proposals for the low-skill visa program back and forth between the unions and the U.S. Chamber of Commerce, a Senate aide said.

“They’re hitting some tough issues balancing business and labor,” said another congressional source. Both spoke anonymously because they are not authorized to speak about the negotiations.

“They’re still working and no one’s thrown anyone over the side. It’s tough stuff, but it’s like a railroad. They’re going down the track and none of the signals are flashing red yet.”

Members of the Senate group had been aiming to advance a joint bill in March. For the first time Tuesday, Graham and Sen. John McCain (R-Ariz.) both said they were uncertain if they would be able to finish the bill before Congress leaves for an Easter recess March 22.

Even if they complete the bill right before the recess, the group is starting to discuss whether it would be wise to put it forward and then immediately leave Washington, ceding the floor to critics to pick it apart during a two-week recess.

“You don’t want to leave it hanging out for two weeks to get shot up,” Graham said.

Republicans involved in the group took pains to stress the path they are discussing would require those who came here illegally to learn English, pay back taxes and get behind those who sought green cards through legal avenues.

The group has also agreed illegal immigrants would not be able to seek permanent residency--the first step to citizenship-- until new border security and enforcement mechanisms are in place. They have envisioned about a 10-year wait for illegal immigrants to seek green cards.

“The best way to understand it is that what people are going to get here, ultimately, after a significant amount of time and after the security measures are in place, the only thing they’re going to get is the chance to apply for a green card,” said Sen. Marco Rubio (R-Fla.).

Still, he said after much thought and going “back and forth” on the issue, he ultimately decided this year to sign on to plans that do allow those here illegally to eventually become citizens. “I just concluded that it’s not good for the country in the long-term to have millions and millions of people who can never, who are forever prohibited from becoming citizens,” he said.

A rising conservative star popular with the tea party--and a potential rival to Bush for the 2016 Republican presidential nomination--Rubio’s central role in the Senate group was underscored Tuesday, as Senate Majority Leader Harry M. Reid (R-Nev.) derisively dismissed Bush’s comments in favor of Rubio’s efforts.

“Frankly, on this issue, I don’t think Jeb Bush is a Florida leader. I think Marco Rubio is. Bush has been elected to nothing lately. Rubio is the leader on immigration,” Reid told reporters.

Discuss this topic and other political issues in the politics discussion forums.