"This effort is too important to be written in a back room and sent to the floor with a take-it-or-leave it approach," McConnell said. "It needs to be done on a bipartisan basis and include ideas from both sides of the aisle."
Sen. Jeff Sessions, R-Ala., said on the Senate floor, "No one should expect members of the Senate are just going to rubber-stamp what a group has met and decided."
Senate Majority Leader Harry Reid, D-Nev., applauded the framework and said, "I will do everything in my power to get a bill across the finish line."
Pressures from outside groups from business to organized labor to immigrants themselves will be immense, even as lawmakers warily eye voters for their reaction.
Besides McCain and Schumer, the senators endorsing the new principles Monday were Democrats Dick Durbin of Illinois, Robert Menendez of New Jersey and Michael Bennet of Colorado and Republicans Lindsey Graham of South Carolina, Marco Rubio of Florida and Jeff Flake of Arizona.
Several of them have worked for years on the issue. McCain collaborated with the late Democratic Sen. Edward M. Kennedy on the comprehensive immigration legislation pushed by then-President George W. Bush that failed in 2007.
The group claims a notable newcomer in Rubio, a potential 2016 presidential candidate whose conservative bona fides may help smooth the way for support among conservatives wary of anything that smacks of amnesty. Rubio has been working with the group while also detailing his own similar immigration proposals to selected media, getting a generally positive reaction from conservative media.
"There are 11 million human beings in this country today that are undocumented. That's not something that anyone is happy about; that's not something that anyone wanted to see happen, but that is what happened. And we have an obligation and the need to address the reality of the situation that we face," Rubio said Monday.
As the group turns to the work of writing legislation, which they hope to see come to a vote in the Senate Judiciary Committee in March, there may be most disagreement over the path to staying in the U.S. legally. To satisfy the concerns of Rubio and other Republicans, the senators are calling for the completion of steps on border security and oversight of those here on visas before taking major steps forward on the path to citizenship.
Even then, those here illegally would have to pass background checks and pay fines and taxes to qualify for a "probationary legal status" that would allow them to live and work here -- and not qualify for federal benefits -- before being able to apply for permanent residency, a critical step toward citizenship. Once they are allowed to apply they would do so behind everyone else already in line for a green card within the current immigration system.
That could be a highly cumbersome process, but how to make it more workable is being left to future negotiations. The senators envision a more streamlined process toward citizenship for immigrants brought here as children, and for agricultural workers.
Outside groups including Latino advocacy organizations, the U.S. Chamber of Commerce and organized labor were quick to praise the emerging framework. But some also sounded notes of caution.
Richard Trumka, president of the AFL-CIO, questioned a proposal by the Senate group to require illegal immigrants to provide proof of employment before they can gain legal status. Trumka said it could exclude millions of workers "who cannot prove employment because they have been forced to work off the clock or have no employer by virtue of being independent contractors."
Deepak Bhargava, executive director of the Center for Community Change, questioned the process being set out for the path to citizenship. "If the details are not done correctly, the path to citizenship can take far longer than it is reasonable. There is real concern about those details," he said.