As immigration soars to an all-time high, that get-tough argument is gaining political steam. With the 2006 elections still 10 months away, a half-dozen candidates are running for national office on pledges to stop illegal immigration. Bills on the issue, many denying benefits to illegal immigrants, have been introduced in 31 state legislatures.

And polls show mounting voter unease about immigration: A December 2005 Wall Street Journal-NBC poll found that 57% of those questioned think the U.S. is "too open to immigrants."

"It's astonishing how much this has become an issue across the country," says Brian Bilbray, a San Diego Republican who hopes to return to the U.S. House of Representatives this year after spending the past six years as a lobbyist for the Federation for American Immigration Reform, which wants to restrict immigration.

But for all the emotion immigration is stirring up, political operatives in both parties warn that it isn't an issue that rallies voters. "Will this impact your electoral ambitions?" asks Ryan Ellis of the conservative group Americans for Tax Reform, who has studied the role immigration played in recent elections. "All history has indicated 'no,' whether you're in Arizona or Maine," he answers.

It didn't prove a successful strategy for the Virginia governor's race in November. Republican Jerry Kilgore seized late in the campaign on the issue of taxpayer-funded job centers for illegal immigrants, and in a stinging television ad asked of his Democratic opponent, "What part of illegal does Tim Kaine not understand?" Although immigration was only one issue in the campaign, Mr. Kaine won with 52% of the vote.

Likewise, in December, in a special House election in California's Orange County -- where illegal immigration is a flashpoint -- Jim Gilchrist, founder of the Minuteman Project, a volunteer border-patrol group, won just 25% of the vote.

Mr. Ellis of Americans for Tax Reform also points to seven 2004 Republican primaries where immigration-restriction candidates never won more than 46% of the vote. Among those beating back challenges: Arizona Congressmen James Kolbe and Jeff Flake, who are sponsors of a House bill that would let illegal immigrants earn legal residency in the U.S.

Candidates who want to restrict immigration seem not to fare well because very few people worry enough about immigration to vote on it -- even though many of them tell pollsters they're worried. In the Wall Street Journal-NBC poll, 78% of those questioned favored "tightening" the border with Mexico -- but only 7% said illegal immigration was their biggest national concern.

Immigration is "a loud debate that produces few voters," says Frank Sharry, director of the National Immigration Forum, a Washington immigrants-rights group.

But that doesn't mean immigration won't be talked about this campaign season. Most prominently among 2006 candidates, Rep. Tom Tancredo, a Colorado Republican, is toying with a symbolic run for the White House. Among other things, Mr. Tancredo wants to deport the estimated 11 million illegal immigrants now in the U.S. and deny citizenship to the U.S.-born children of illegal immigrants.

Immigration restrictionists also have announced runs for governor in Colorado, for the U.S. Senate from California and for a smattering of House seats. San Diego's Mr. Bilbray is running in an April primary to succeed former Rep. Randall "Duke" Cunningham while also pursuing a class-action lawsuit that would prevent California public colleges from offering in-state tuition to illegal aliens.

Some state legislatures are considering extending in-state tuition, health benefits and driver's licenses to illegal immigrants, even while others want to ban such benefits. In Ohio, a statehouse Republican has said he is considering an amendment to the U.S. Constitution to exclude illegal immigrants from the census counts that are used to apportion Congressional seats.

Bills in New Hampshire and North Carolina would require local policemen to enforce federal immigration laws, and one in Virginia would require proof of legal residency to obtain a marriage license.

With Republicans largely leading the anti-immigration charge, the issue is causing heartburn for the national party, which was hoping that its generally pro-immigration stand would help it pick up Hispanic voters. Twelve years ago, California's Republican Gov. Pete Wilson won re-election in part by campaigning for a ballot measure that would deny benefits to illegal aliens -- a rare instance where an anti-immigration stand won the day.

But a decade passed before Republicans won the governor's office again, and they still haven't won back Hispanic voters. "It was a metaphor for short-term gain, long-term loss," says the National Immigration Forum's Mr. Sharry.

Republican pollster Ed Goeas says he urges his clients to talk about solutions to illegal immigration instead of focusing on emotion-charged issues like immigrant job centers if they want to win. His firm, the Tarrance Group, does polling for several immigration-restriction candidates, including Mr. Tancredo, he says.

But in anticipation of the 2006 elections, he's also running voter focus groups to help candidates handle such volatile issues as amnesty for illegal immigrants and whether to allow guest workers to eventually stay in the U.S. After voters let off steam, he says, focus groups show that immigration "becomes a very reasoned conversation very quickly."

Write to June Kronholz at june.kronholz@wsj.com