Advocates, lobbyists, and wonks are now convinced Congress will try to tackle the issue. But they still know that any bill will have to run a gauntlet.

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Keith Bedford/Reuters

This is actually happening. That's the viewpoint of Capitol Hill aides, lobbyists, advocates, and politicians who have been involved in the immigration debate for 10, 20, and in some cases 30 years. They are psyched. They are scared. They are sober.

They miss the late Senator Edward Kennedy, D-Mass., who has been at the forefront of every immigration law since 1965. They are grateful for Senator Marco Rubio, R-Fla., who has spurred a new way of thinkingabout immigration among conservatives.

This account is based on interviews with more than a dozen people close to the immigration talks on Capitol Hill and in the White House.

President Obama's speech on Tuesday in Nevada will mark the public unveiling of private planning that has been in the works at the White House and in Congress for at least a year. Administration officials have mulled every possible option for easing the paradox of too many illegal immigrants and a stilted legal system. The only real solution is broad legislation.

No one knows how it will end. The public statements from Obama and a group of bipartisan senators will reflect a possible resolution to years of conflict and confusion. The contours of the deal are so simple that a Martian visiting the United States would wonder why politicians have been fighting about it for 15 years. There will be some type of earned legalization for illegal immigrants, an ironclad way for employers to verify that their employees are legal, a smooth visa system for future immigrants, and robust border security.

Everyone with a stake in the outcome fears that a misstep on the part of one political party will offend the other party and blow up the deal. Two old hands at the debate, Senators John McCain, R-Ariz., and Robert Menendez, D-N.J., were extremely careful on ABC's This Week on Sunday talking about immigration. McCain said he wanted Obama's help. Menendez said Obama would work with Republicans. Liberals fear that Obama will be too dictatorial when he spells out his immigration reform plan. If his tone isn't deferential enough, it could alienate Republicans whose support is needed for anything to pass. Conservatives fear that Democrats don't actually want an immigration reform bill and would rather make Republicans look bad by alienating Hispanics.

Whatever happens, it will play out in a big way. Senate Majority Leader Harry Reid has designated immigration legislation with the bill number S.1, a signal the bill is the top Senate priority. (He did the same thing for Obama's health-care bill.) The Senate Judiciary Committee is expected to begin crafting it in February. It should be on the Senate floor in May or June.

Lengthy congressional debates of this sort are public and messy. Drafters of the bill will have their hands full keeping the amendment process from sinking the effort. The White House will need to keep up the pressure without scaring away skittish Republicans. It's a delicate dance that has never been attempted without Kennedy.

Advocates expect to lose at least five Democrats in the Senate, which means they will need upwards of a dozen Republicans to vote for the legislation. That's where Rubio and other Tea Party favorites like Senator Mike Lee of Utah will come into play. Rubio and Lee are newcomers to an old discussion among Republican veterans like McCain and Senator Lindsey Graham of South Carolina. Newly elected Senator Jeff Flake of Arizona will be a key Republican player as well.

Conservative senators who want an immigration bill will be pitted against fellow conservatives who don't, like Senators Charles Grassley of Iowa, Jeff Sessions of Alabama, and David Vitter of Louisiana. To get past their own party's naysayers, Republicans could make demands that are unpleasant, if not unpalatable, for traditional Democrats.

Next comes the House, where Judiciary Committee Chairman Bob Goodlatte, R-Va., is in no hurry to rush any broad legislation. Goodlatte's main objective is much more modest -- to familiarize his committee members with immigration policy such that they understand the difference between a work visa and a green card. There are not enough Republican votes in the House to pass anything that would earn Obama's signature or the nod from Senate Democrats.

So how can a sweeping immigration bill actually pass? Supporters from both parties are acutely aware that missteps in a few crucial areas could derail the effort. But they also sense a new political reality pushed into sharp relief by November's election -- the stalemate on immigration has to end. Republican strategists want nothing more than to remove the issue from their plates. The only way that happens is if a bill passes.

There are three main hurdles to passing an immigration bill -- citizenship, guest-workers, and House Republicans. Any one of them could scuttle the prospects of passage, but all are surmountable.

Citizenship. A bizarre shift occurred in the last year when Rubio emerged onto the national scene and begged fellow conservatives to speak more positively about immigration. The sparring that used to be about "amnesty," or legalizing illegal immigrants, is now about granting them citizenship. Rubio and former House Speaker Newt Gingrich are among the conservatives who have protested any law that gives illegal immigrants their own method of becoming citizens.

That's fine, say White House officials and congressional Democrats. They aren't asking for a special path to citizenship. They just want it to be possible for non-criminal undocumented immigrants to live legally in the United States and use regular methods to become citizens within a reasonable amount of time. "Reasonable" is subject to negotiation -- 10 years? 20 years? No one disputes that the illegal immigrants need to be "at the back of the line." The negotiation is basically a matter of logistics unless Republicans refuse to allow any way for illegal immigrants to become citizens. Then it's over.

Guest-workers. Conservatives are worried that unions will sink the immigration deal by flatly opposing any bill that has a guest-worker component. Democrats and unions are wary of guest-worker programs because they fear that Americans will lose out on job opportunities and working conditions will slide. In the past, the business community and Republicans have insisted that any comprehensive immigration fix include guest-worker visas.

The weak economy has made this conversation easier. "Guest-worker" is a dirty word in business circles. It has now in vogue to talk about permanent green cards for skilled foreign workers, a topic far less inflammatory for unions. There is a dedicated consortium of influential employers who are willing to throw serious lobbying heft behind more green cards for foreign engineers and scientists. Obama and the bipartisan group of senators will probably make a big deal about the need for skilled workers at first and save the trickier question of temporary visas for low-skilled employees for a smaller stage. (Like, say, at the end of a 12-hour markup in committee.)

House Republicans. No one expects "regular order" in the House on immigration. Any broad bill that comes to the floor under normal proceedings would certainly be doomed. The House has killed Senate immigration legislation before (in 2006), and forces are gathering to do so again. The Judiciary Committee counts several bomb throwers as members; Rep. Steve King, R-Iowa, is the most well known in immigration circles. The committee also includes ruby-red conservatives like Rep. Jim Jordan, R-Ohio, whose actions are closely scrutinized by other Republicans. Its former chairman, Rep. Lamar Smith, R-Texas, is feverishly opposed to increasing immigration, particularly for low-skilled workers.

But that doesn't mean an immigration bill can't get through. A bipartisan group of House lawmakers has been quietly working on an immigration bill that would satisfy conservatives and liberals. The Republican participants are a closely-held secret, but whisperers say they include serious conservatives like Paul Ryan of Wisconsin, Ted Poe of Texas, and Raul Labrador of Idaho. House Speaker John Boehner is among the Republicans who desperately want the GOP's hand-wringing on immigration to end. He has already demonstrated that he is willing to flout party rabble-rousers with the House's recent votes on fiscal cliff taxes and Hurricane Sandy, which passed with more Democrats than Republicans.

Boehner has to be careful. He only has so many chances to put incendiary legislation on the floor before his caucus stages an all-out revolt. To appease them, he will probably offer one or two high-profile House votes, where Democrats will protest like crazy, on enforcement-only immigration legislation. That gets the dealmakers to the next step, a conference committee where anything can happen. As Kennedy was fond of saying, "We'll fix it in conference."

If Boehner wants the issue to go away, he might be willing to put a conference report up for a vote despite a raucous caucus. It's possible that enough Republicans could join with Democrats to support it.

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