Has the Republican presidential race been getting any clearer? Actually, no. It's been getting muddier. And the fallout from the collapse of the Senate immigration deal makes it muddier still.

Former New York City Mayor Rudy Giuliani is the GOP front-runner. But instead of picking up speed, he's been slowing down. Giuliani's support averaged 37 percent in four national polls of Republican primary voters conducted in March. He averaged 36 percent in four April polls, and 30 percent in seven polls taken in May.

Is anyone catching up with Giuliani? Not really.

Sen. John McCain of Arizona has picked up a few points, but he remains firmly in second place, averaging 22 percent in the May polls. Former Sen. Fred Thompson of Tennessee hasn't even formally declared, but he's already running third—with a May average of 12 percent. And former Massachusetts Gov. Mitt Romney? If slow but steady wins the race, watch Romney. His numbers have been creeping up—averaging 8 percent in March, 9 percent in April, and 10 percent in May.

None of the other contenders has averaged more than 2 percent over the past three months.

The GOP usually nominates its heir apparent, but this time it doesn't have one. No one is carrying the Bush administration's banner.

And most of the candidates sound as if they don't want to. "We did not do a great job after we knocked down Saddam Hussein," Romney said during the New Hampshire debate. McCain told a voter who lost her brother in Iraq, "This war was very badly mismanaged for a long time, and Americans have made great sacrifices, some of which were unnecessary because of the mismanagement of this conflict."

Rep. Tom Tancredo of Colorado said, "I have been so disappointed in the president in so many ways for the past several years, not just over the immigration issue but other things." Tancredo recalled that Karl Rove had warned him that because of his criticism of President Bush, he should "never darken the doorstep of the White House." As president, Tancredo said, "I would have to tell George Bush exactly the same thing."

Many conservatives are suspicious of all the leading contenders. Romney, who has shifted his views on social issues, said, "I am not going to apologize for the fact that I became pro-life." Giuliani tried to take both positions at the same time: "My view on abortion is that it's wrong but that, ultimately, government should not be enforcing that decision on a woman."

McCain has picked fights with conservatives, most recently by championing an immigration bill that is deeply unpopular with the base. Tancredo said that McCain, by backing the Senate bill, rang the "death knell" for his candidacy. "It probably means there will never be a President John McCain," Tancredo said on Iowa Public Television.

The fact that the bipartisan immigration deal collapsed in the Senate, with Republicans voting 38-7 against cloture, looks like a failure of leadership—by President Bush, certainly, but also by McCain, who was a principal architect of the deal. On the other hand, if the bill is dead, the controversy could drop out of the headlines. It would certainly be in McCain's interest for the campaign to move on.

The problem of illegal immigration is not going away, however. Senate Majority Leader Harry Reid, D-Nev., said on the Senate floor, "We're finished with this—for the time being." After the deal fell through, McCain said, "It's not over. We still have broken borders, and we still have this problem of not finding out who these people are."

For many Americans, the deal's collapse brought frustration, not satisfaction. The system failed. McCain is running on a promise that he can fix the system. "It's our job to do the hard things, not the easy things," McCain said in the New Hampshire debate.

McCain's position on immigration, like Giuliani's on abortion, raises yet another complicating factor for Republicans. If McCain or Giuliani gets the Republican nomination, it could spur a conservative to run as an independent, damaging the Republicans' chances of keeping the White House.