Senators, who have been arguing for weeks over provisions of the compromise immigration bill, are set to decide today whether to close debate and vote on passage. Whatever happens, the fate of the immigration bill is likely to have consequences for both parties in the 2008 presidential election.

The Times’s Robert Pear reports that the “outlook for the bill remained in doubt” after senators considered a slew of amendments yesterday. Supporters of the bill say if they can muster the 60 votes needed to close debate, passage would be likely.

But, already three moderate Democrats — Senator Claire McCaskill of Missouri, Jim Webb of Virginia and Jon Tester of Montana – have indicated they are balking at the bill.

Meanwhile, the immigration debate has been generating a flood of phone call, e-mails and, as The Time’s Jeff Zeleny reports, at least a few threats to members of Congress: “Not since the impeachment of President Bill Clinton, several Senate aides said, have the lines been so jammed by a single issue.”

Arizona Governor Janet Napolitano, a Democrat, flew to Washington this week to lobby for the bill’s passage. She “warned her party that failure to deal with immigration this year could hurt Democrats in next year’s presidential race”:

“If there’s no bill, it spills into the presidential election in a major way,” Napolitano said. “I would suggest to presidential candidates, Democrat and Republican alike, that … if you’re going to say something besides the word amnesty, it is a hard issue to deal with in the sound-bite nature of a presidential campaign. If I were the presidential candidate, I would want the Congress to move on a bill, so that my sound-bite is, ‘I’m going to enforce the law that the Congress just passed, and make sure that we get the resources to enforce it.’ “

The senior senator from Ms. Napolitano’s state, John McCain, is likely hoping for a chance to use that sound-bite in the presidential race. While his campaign is trying to portray his unwavering support for the immigration bill as an example of his principled leadership, even some of his closest advisers acknowledge their concern.

“From a political perspective, having a candidate that takes on all the tough issues is not always the most politically expedient thing to do,” said David Roederer, the chairman of McCain’s campaign in Iowa. Asked what he would like to see happen on immigration, Roederer laughed and said: “Wind the clock back and forget that this issue ever came up?”

The clock is ticking on the June 30 campaign finance reporting deadline, and the presidential campaigns, finding they have tapped out some of their high rollers, are now turning to smaller donors to fill their campaign war chests.

The Chicago Tribune’s political blog, The Swamp, reports that the campaign of Illinois Senator Barack Obama, is saying that it has received contributions from nearly a quarter-million people so far this year.

While all eyes will be on the action in the Senate during the day, tonight the Democratic presidential candidates appear at Howard University for a forum aimed at minority voters. Talk show host Tavis Smiley moderates the discussion that will be broadcast on PBS beginning at 9 p.m.

The top Republican candidates gather for a forum of their own in Iowa this weekend. Representative Ron Paul, who is vying for the Republican nomination, was not invited to participate, so he’s decided to hold his own forum right next to the main event.

One debate that has already been playing out on the airwaves this week is the one between the campaign of former Democratic Senator John Edwards and conservative commentator Ann Coulter. In case you missed the verbal sparring, The Times’s Adam Nagourney has the details.

Washington Post columnist Dana Milbank thinks New Mexico Governor Bill Richardson might actually be running for something other than president.

Following Republican presidential candidate Rudolph W. Giuliani around on the campaign trail, the Los Angeles Time’s Maria L. La Ganga, picks up on one of the former New York mayor’s most consistent campaign themes: terrorism.

Bloomberg’s Kim Chipman and Julianna Goldman trace former Tennessee Senator Fred D. Thompson’s path from small-town lawyer to United States senator to the brink of a presidential run. But, Mr. Thompson’s supporters wonder “whether he wants it badly enough to endure the rigors of a campaign.”

The Times’s Susan Saulny, who followed Mr. Thompson to South Carolina yesterday, reports that, like the actor he is, Mr. Thompson is practicing his lines for his campaign’s expected debut.