He drew the biggest applause from his invited audience when he spoke about illegal immigrants: “A lot of folks forget that most of us used to be them.”

“Si se puede!” they chanted, roughly, “Yes, it can be done.”

Another potential boon to the prospects is the support of organized labor. Several union leaders including AFL-CIO President Richard Trumka attended Obama’s speech, signaling their support. In past efforts to pass reforms, labor unions have been wary of comprehensive legislation that called for large expansions of guest-worker programs, which they called abuses of the guest-worker programs and unfair competition to American laborers.

Senate Minority Leader Mitch McConnell, R-Ky., said it would be foolhardy to calculate the immigration proposals put forth by Obama and senators without seeing the plans in legislative form.

“I’ve got a good indication that there’s a bipartisan desire to go forward,” he said. However, McConnell said, “I think predicting how one is going to vote on this package before it gets out of committee is something I’m not prepared to do.”

And there remains a question of how the House of Representatives will act.

Speaker John Boehner, R-Ohio, who has said he wants to tackle the issue this year, warned Obama to not get too partisan.

“There are a lot of ideas about how best to fix our broken immigration system,” Boehner spokesman Brendan Buck said. “Any solution should be a bipartisan one, and we hope the president is careful not to drag the debate to the left and ultimately disrupt the difficult work that is ahead in the House and Senate.”

Memories of the amnesty legislation of 1986 continues to haunt many Republicans. President Ronald Reagan signed that bill into law amid many of the same promises to grant legal status to illegal immigrants, clamp down on unscrupulous employers and finally secure the border. Instead, the border remained porous, companies continued to hire illegal immigrants, and illegal immigration exploded.

“The president has demonstrated he will only enforce the laws that he likes,” said Rep. Steve King, R-Iowa. “Promises of future law enforcement made under the 1986 Amnesty Act were not adequately kept by President Reagan. Why, then, would Americans accept the promise of this president?”

In 2007, a Senate plan that included a pathway to citizenship died despite backing from President George W. Bush and other Republicans. In 2010, negotiations broke down in the Senate before a plan could be completed as many states began tackling illegal immigration themselves.

“The last time Congress tackled major immigration reform, it took nearly 10 years from the time the first bill was introduced in 1981 until legislation was finally enacted in 1990,” said Stephen Yale-Loehr, an immigration law expert at Cornell University. “Moreover, Congress operated more efficiently then. I doubt immigration reform legislation will be enacted this year, but I hope I am wrong.”

Kumar reported from Las Vegas, Ordonez from Washington. William Douglas of the Washington Bureau contributed.