October 2007 may turn out to be the month that immigration became a key issue in presidential politics. It hasn't been, at least in my lifetime.

The Immigration Act of 1965, which turned out to open up America to mass immigration after four decades of restrictive laws, wasn't one of the Great Society issues Lyndon Johnson emphasized in 1964. The Immigration Act of 1986, which legalized millions of illegal immigrants but whose border and workplace provisions have never been effectively enforced, was a bipartisan measure unmentioned in the debates between Ronald Reagan and Walter Mondale.

There was no perceptible difference on immigration between George W. Bush and Al Gore in 2000. Both favored a comprehensive bill with legalization and guest-worker provisions. John Kerry in 2006 and 2007 voted for immigration bills along the lines supported by Bush.

Now, things look different. In the Democratic debate on Oct. 30, Tim Russert demanded to know whether Hillary Clinton supported New York Gov. Eliot Spitzer's policy of issuing driver's licenses to illegal immigrants. The forthright answer: yes and no. A clarifying statement by the Clinton campaign later in the week did not much clarify things: a hedged yes. It was one of several issues on which Clinton seemed to take calculating and ambiguous non-positions. But it is one that may have major reverberations in the presidential campaign -- and in congressional races, as well.

The reason is that the Democrats -- and Bush -- are out of line with public opinion on the issue. That became clear as the Senate debated a comprehensive immigration bill in May and June. Most Republicans and many Democrats, in the Senate and among the public, turned against the bill. Supporters of the bill tended to ascribe that to something like racism: They just don't like having so many Mexicans around.

But if you listened to the opponents, you heard something else. They want the current law to be enforced. It bothers them that we have something like 12 million illegal immigrants in our country. It bothers them that most of the southern border is unfenced and unpatrolled. It bothers them that illegal immigrants routinely use forged documents to get jobs -- or are given jobs with no documents at all.

You don't have to be a racist to be bothered by such things. You just have to be a citizen who thinks that massive failure to enforce the law is corrosive to society.

That was apparent to me as I listened to a focus group of Republican voters in suburban Richmond, Va., conducted by Peter Hart for the Annenberg School of Communications. One voter after another complained that the immigration laws were not being enforced. None of them made any derogatory remarks about Latino immigrants -- two said they admired how hard they work. They don't want to see Latinos banished from this country. They want the immigrants here to be legally here.

Which leaves Democratic politicians and political candidates out on a pretty flimsy limb. Most of them reflexively back a comprehensive bill, and some of them (like Bush and a number of Republicans backing such a bill) have dismissed opponents as racists.

Most Democrats have also been backing bills extending various benefits to illegal immigrants, like the Dream Act for college education for illegals brought over as children. There are appealing arguments for such bills. But most voters reject them. And most voters certainly reject driver's licenses for illegal immigrants. That was one of the issues that led to the recall of Gov. Gray Davis in California in 2003.

The Republican presidential candidates have taken note. Only John McCain, a longtime backer of a comprehensive bill, stands apart, and he concedes that voters are demanding tougher enforcement. In the special congressional election in Massachusetts on Oct. 5, the Republican was able to hold the Democrat to 51 percent by stressing immigration as one of his two top issues.

Other Republicans are likely to echo that theme next fall. And the Democratic presidential nominee (unless Chris Dodd gets the nod) is going to have to explain why she or he believes it's a good idea to give illegal immigrants driver's licenses.

The last several Democratic nominees could have said that they're just taking the same position as their Republican opponent. The 2008 nominee won't be able to say the same of hers or his (unless McCain gets the nod).

"The centrality of illegal immigration to the current discontent about the direction of the country may be taking us back again to a welfare moment," write the shrewd Democratic strategists James Carville and Stanley Greenberg. Yup.