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That ad is sponsored by the Service Employees International Union’s Committee on Political Education and by Priorities USA, a super PAC run by a former Obama staffer.

The campaigns themselves are staying more positive in their Spanish-language pitches.

Mr. Obama is running commercials featuring Cristina Saralegui, whom some papers have labeled the “Latino Oprah,” in which the talk show host says Hispanic voters should reward the president for signing the health care legislation and for his work to revive the economy.

“It makes me laugh when some say that President Obama has done nothing,” she says in Spanish in the ad.

Mr. Romney has run ads featuring his son Craig telling voters in Spanish that the candidate’s father, George Romney, was born in Mexico. Craig Romney also said his father would work toward a long-term solution to the nation’s immigration system.

Mr. Aguilar said Republicans do have problems reaching Hispanic voters, but that the Romney ad is a solid effort.

“That is an ad that can have impact because, again, it says to Latinos, [the president] failed you and is not willing to work with Republicans. My dad hasn’t had a chance. He’s willing to,” Mr. Aguilar said.

Ms. Tramonte, though, said the spot tries to hide Mr. Romney’s stances from the primary campaign, such as his support for Arizona’s crackdown on illegal immigration.

“President Obama has a pretty good response to those ads, which is, he’s the only one who’s taken action to try to do something on immigration in the last four years,” Ms. Tramonte said.

Nevada, where Mr. Aguilar’s group is running its ads, is a hot spot for immigration politics, and the debate is playing out in the state’s Senate race, too, where Ms. Tramonte accused Sen. Dean Heller, a Republican, of tailoring his immigration message for Spanish and English audiences on his Web page.

The Republican incumbent’s English page includes an “immigration” section that says Mr. Heller wants to enforce existing immigration laws and boost the Border Patrol, and that he opposes “amnesty.”

But his Spanish-language page, which is part of the main website, doesn’t talk about enforcement and instead focuses on fixing the difficulty of navigating the legal immigration system.

Mr. Heller’s spokeswoman, Chandler Smith, said the senator doesn’t try to hide his stances.

“Dean Heller has been open and honest with the Hispanic community about his position on a wide range of issues, including immigration reform. He is not afraid of this discussion,” the spokeswoman said. She said Democrats are turning to immigration as an issue to try to recapture Hispanic voters who are backing Mr. Heller over his Democratic challenger, Rep. Shelley Berkley.