This year's election is likely to be the first in which illegal immigration is a national issue. Which party will benefit? That's not clear.

One thing is clear: Critics of illegal immigration are energized and motivated throughout the country, even in states far from the Mexican border. Take Tennessee, whose Republican Senate candidate, Ed Bryant, worked with the Minutemen in Arizona to repair a border-security fence. "There can be no amnesty for people who come into this country illegally and break the law," Bryant said. "I don't care what you call it—'pathway to citizenship,' or whatever. That's still amnesty."

The politics of the issue are complicated. In a CNN poll taken by the Opinion Research Corp. last month, 79 percent of Americans said they support a path to citizenship for illegal immigrants who have been in the United States for a number of years, have a job, and pay back taxes. But those who oppose that policy are more intensely motivated: 43 percent of opponents say the issue will be "extremely important" to them when they vote this year, compared with 24 percent of those who favor a path to citizenship.

Republicans around the country are facing a hostile political environment, and many believe that the issue of illegal immigration will help them survive. This group includes Gov. Tim Pawlenty, who is running for re-election in Minnesota. Pawlenty has proposed to set up a team of Minnesota state agents to enforce federal immigration laws. He recently described his opponent as "one of the big-spendin', tax-raisin', abortion-promotin', gay-marriage-embracin', more-welfare-without-accountability-lovin', school-reform-resistin', illegal-immigration-supportin' Democrats."

Republican Sen. Jon Kyl of Arizona also takes a tough line on border enforcement. His Democratic challenger, Jim Pederson, is fighting back. Pederson invokes the name of Arizona's other Republican senator, John McCain, to criticize Kyl. One Pederson TV ad quotes McCain as saying that Kyl's suggestion that illegal immigrants should have to return to their home countries before applying for temporary work permits "borders on fantasy." Kyl voted against McCain's immigration bill. But McCain happens to be Kyl's campaign chairman.

Immigration was a big issue in last week's special election in California's 50th Congressional District, 30 miles from the Mexican border. Republican Brian Bilbray ran as a staunch opponent of illegal immigration; on the ballot, he listed his occupation as "immigration reform consultant." His Democratic opponent, Francine Busby, tried to link "lobbyist" Bilbray to the district's disgraced former Republican congressman, Randy (Duke) Cunningham.

In the end, immigration trumped corruption. Bilbray held the district for the GOP, although the vote was close (49 percent to 45 percent, in a district that had voted 58 percent for Cunningham and 55 percent for George W. Bush in 2004). The message to Republicans around the country was clear: You may be able to save yourself by defying President Bush on immigration. Bilbray explained his winning strategy: "I said, 'Don't blame the House of Representatives and Brian Bilbray for the mistake that the Senate and the president were making [on immigration].' It made all the difference in the world."

What about all those protest marchers who came out in the spring to defend immigration rights? Are pro-immigration forces having an impact anywhere?

In Connecticut, Republican Christopher Shays's vote in favor of the tough House immigration bill has drawn criticism. Shays represents an upscale, socially moderate district. Democrats are also hoping to make the House bill an issue against Republican Ric Keller in Florida; his district includes a large number of Cuban-Americans.

California Gov. Arnold Schwarzenegger is trying not to alienate his state's sizable Hispanic vote. He responded slowly and cautiously to President Bush's request to send National Guard troops to the border, telling an interviewer, "When [Homeland Security Secretary Michael] Chertoff called, the idea of sending National Guards to the border was half-baked, and I told him that." The governor added, "I think for them, maybe, it was baked."

The illegal immigration issue is splitting both parties and generating protest candidates throughout the country. That makes the political impact of the issue highly uncertain.