As hard as it was in the Senate to pull together a winning coalition on immigration reform, getting to "yes" with the House - in a form that can again pass both bodies - will be even tougher.
But it's not impossible. Even before the Senate completed work on its immigration bill Thursday, House Republicans were signaling an openness to compromise, as long as the final legislation maintains a focus on border security.
"I believe it is resolvable, and we will be successful in putting an illegal immigration bill on the president's desk," said House majority leader John Boehner, before the Senate vote Thursday. But he cautioned: "This is going to be a delicate negotiation between the House and Senate."
On some fronts, the way forward is obvious. Both the House and Senate bills include measures to improve border security. The House bill proposes building 700 miles of fence along the border with Mexico; the Senate bill, 370 miles.
But the guest-worker program and a path to citizenship for millions of people in the US illegally are sticking points for many House Republicans. Their position is that any form of amnesty is unacceptable.
"We shouldn't be selling American citizenship," Rep. James Sensenbrenner (R) of Wisconsin said Sunday on CBS's "Face the Nation." "What the Senate is doing is it is providing illegal immigrants benefits that we don't give to legal immigrants, and that's dead wrong."
Moreover, House leaders say that unless a compromise plan has the support of most House Republicans, it will not be allowed to come to a vote - even if the members of the conference committee agree on a compromise.
"The Speaker will not bring a conference report on immigration to the floor unless it has the support of a majority of the majority," says Ron Bonjean, spokesman for Speaker Dennis Hastert.
GOP leaders are hopeful that threshhold can be met, he adds. "This will be a difficult conference, but the Speaker believes we can get to a balanced bill that will put border security first."
This week, President Bush's top political adviser, Karl Rove, made his second trip to Capitol Hill to boost prospects for a compromise. While several Republicans who spoke with the press after the closed meeting said they were not convinced, others are signaling they may be interested in helping to broker a deal.
On Tuesday, Rep. Mike Pence (R) of Indiana, leader of the Republican Study Group, proposed a privately operated guest-worker plan in a talk before the Heritage Foundation, a conservative think tank.
"I agree with the president that a rational middle ground can be found between amnesty and mass deportation, but I disagree with the president that amnesty is the middle ground," he said. The solution, Representative Pence said, is to set up a system that "will encourage illegal aliens to self-deport and come back legally as guest workers." Under this plan, the federal government would license private worker-placement agencies to match willing guest workers with jobs that cannot be filled with American workers.
Meanwhile, the Republican Main Street Partnership, a group of moderate Republicans in the House and Senate, is offering to help broker a deal. Last weekend, Rep. Michael Castle (R) of Delaware and Sen. John McCain (R) of Arizona, both Main Street members, opened discussions on the bill.
Senate conservatives, however, are urging their House colleagues to hold the line against amnesty and for border protection.
Commenting on the Senate immigration bill, which had not been passed at press time, Sen. Rick Santorum (R) of Pennsylvania said: "This [bill] is not acceptable to me, and I hope that the House of Representatives thinks the same way. This is not what I would expect from a country of laws."
Sen. John Cornyn (R) of Texas, already designated as a conferee who will meet with House conferees, says he remains committed to comprehensive reform and thinks it can be achieved in the conference.
"I am concerned that we still have not learned the lessons of [immigration-law overhaul in] 1986, which resulted in massive fraud and [in] the federal government refusing to provide the information needed for enforcement" of sanctions against employers who hire illegal immigrants.
The House bill, which passed in December, addresses only border protection and illegal immigration "control." Mr. Bush and a bipartisan coalition in the Senate want border control plus an expanded guest-worker program and a path to legalization for most of the 11 million people in the country illegally.
Many GOP lawmakers worry that voters in November will punish legislators who back any measure that appears to reward illegal behavior. Rep. Tom Osborne, who ran in the Nebraska Republican primary for governor, lost his bid after an ad campaign criticized his support for in-state tuition for children of illegal immigrants.
More registered Republicans (19 percent) cite immigration as the most important national problem than cite any other issue, according to a Pew Hispanic Center poll this month. Only 6 percent of Demo-crats cite it as the most important problem.