IN 2004, THE NEW hotbed of Republican voters was the outer suburbs, the so-called exurbs on the distant outskirts of a central city, packed with tract housing, strip malls, chain stores, a megachurch or two, and thousands and thousands of middle class and lower middle class families. President Bush romped in the exurbs. He won 97 of the 100 fastest-growing counties in America--most of them exurbs--and piled up a 1.72 million vote advantage over John Kerry.

From the governor's election in Virginia last week, there's a bit of evidence that the Republican grip on the exurbs may be loosening. Jerry Kilgore, the Republican candidate for governor, lost Loudoun and Prince William counties, exurbs that Bush won handily last year and that Republican Mark Earley, who lost the governor's race in 2001, won by a wide margin.

The evidence of a serious falloff is not overwhelming, for sure. The two counties are unique in that they're on the fringe of Washington, D.C., and thus voters may have been influenced by national trends and the floundering of President Bush and congressional Republicans. Moreover, these voters may have been affected by the coverage of the governor's campaign in the Washington Post, which was highly favorable to the Democratic candidate, Tim Kaine, and hostile to Kilgore.

Still, the outcome in Loudoun and Prince William should be alarming to Republicans. Located west of Washington, Loudoun is the second fastest-growing county in the country. Kilgore lost Loudoun by 51 percent to 46 percent. A year earlier, Bush did 10 points

So what's the cause of the dip? It's largely a matter of guesswork. Ken Mehlman, the Republican national chairman, thinks independent voters, deciding at the last minute, went with "how they felt things were going." And since polls show a large majority of Americans believe the country is headed in the wrong direction, they voted for the opposition party's candidate, Kaine. They turned with the political wind.

Maybe, but I think there are two better explanations for the Republican retreat in the two exurban counties. First, there's the immigration issue. Late in the campaign, Kilgore played up his opposition to government aid for illegal immigrants. He did so in TV ads and speeches, criticizing Kaine for supporting taxpayer-financed services for illegals and their families. The tagline in his TV spots was: "What part of 'illegal' does Tim Kaine not understand?"

The question is not whether Kilgore was indulging in blatant immigrant-bashing. He wasn't. The question is whether his emphasis on illegals might have been seen as unfriendly to immigrants, especially by the large immigrant communities in the two counties. An exit poll might have answered this question, but none was conducted.

Nevertheless, Republican consultant Jeffrey Bell insists the immigrant issue hurt Kilgore. Attacks on immigration work in theory but often not in practice. Bell says criticizing illegal immigrants has backfired in every campaign he's familiar with that emphasized the issue. Indeed, the Kilgore campaign was slipping in the polls late in the campaign when he was highlighting the immigrant issue.