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For months, Republicans have said they see an opening by using Mr. Chavez. The strategy is based in part on the success Mexican President Felipe Calderon had in winning his country’s 2006 election by demonizing Mr. Chavez.

Mr. Calderon, who had initially trailed in polls, began deploying ads tying his chief opponent Andres Manuel Lopez Obrador to Mr. Chavez, and analysts said the attacks flipped the polls around, giving Mr. Calderon a slim victory.

But Luis Fraga, a professor at the University of Washington and one of the principal investigators in the Latino National Survey, a compendium of data about Hispanic voters, said the Chavez attack ad won’t have much effect here.

“Separate from immigration-related issues, there is no consistent evidence that issues in Latin America have a great impact on the political preferences of Latino voters in the United States,” he said.

He said Hispanic voters in the 2006 study ranked issues facing the country about the same way as other voters did. But asked which issues were most important to Latino voters in particular, a plurality chose immigration.

The issue is so volatile it’s been the subject of harsh ads in the Spanish-language market.

Despite Mr. McCain’s clear leadership on, and Mr. Obama’s support for, a bill legalizing illegal immigrants, each man has blasted the other for not doing enough.

Mr. McCain and the Republican National Committee have accused Mr. Obama of supporting amendments that scuttled the immigration agreement.

Mr. Obama replied with an ad linking Mr. McCain to talk-radio host Rush Limbaugh, who fought the senator’s immigration proposal.

“They made us feel marginalized in a country we love so much,” the ad says, pointing to “insults” it says were tossed at Hispanics.

Mr. McCain has said he now supports certifying the borders are secure before going ahead with another attempt at legalization. Mr. Obama says security and legalization must be part of the same package.

Mr. Obama has seen prominent Hispanic supporters of Mr. Obama’s nomination rival, Sen. Hillary Rodham Clinton, announce support for Mr. McCain. One of them, Luchy Secaira, a former superdelegate for Mrs. Clinton, said she doubts Mr. Obama’s strength among Hispanic voters.

“I was on the ground, and I think all this support is just smoke and mirrors. I don’t think he enjoys overwhelming support in the Hispanic community, as does John McCain,” she told reporters in endorsing the Republican yesterday on a conference call arranged by the McCain campaign.