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As voters in Arizona and Michigan were voting in their states’ GOP primaries Tuesday, Democrats fired another round of criticism about front-runner Mitt Romney and what they say is his hostility to Latinos.

A week after President Barack Obama and the Democratic National Committee focused their GOP-targeted criticism on the former Massachusetts governor and his hard line on immigration, other Democratic leaders are keeping alive the message to Latinos that a Romney presidency would be detrimental to Latinos.

Polls in the last week have showed Romney virtually tied with rival Rick Santorum in Michigan, where Romney was born.

But in Arizona, where they also were in a dead heat last week according to some polls, Romney had achieved a comfortable lead over Santorum, a former U.S. Senator from Pennsylvania. His Arizona lead is attributed in part to his tough stand on illegal immigration.

He picked up the endorsement of Arizona Gov. Jan Brewer on Sunday, and did well in the state's GOP presidential primary in 2008.

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At stake Tuesday are 29 delegates in Arizona and 30 in Michigan. The close race in Michigan overshadowed the primary in Arizona, but the dynamics of the campaign in Arizona has made it more watched by Latinos nationwide.

“Mitt Romney may feel good about his looming primary win amongst extremist Arizona Republicans, but that win is going to come at huge costs,” said Rebecca Acuna, spokeswoman for the Texas Democratic Party, in a statement. “Mitt Romney’s perfected the art of alienating Latino voters. The fact that he was endorsed by former [California] Governor Pete Wilson foreshadows the inevitable doom of his campaign.”

As the GOP primary has emphasized conservatism, and candidates seeking to be their party’s nominee have been in fierce competition to claim the label “most conservative,” immigration emerged as a key issue in their debates and the campaign trail.

Romney has stood out as the most hard line on immigration, not necessarily because his positions are dramatically different from those of Santorum, former Speaker Newt Gingrich and Texas Rep. Ron Paul, but because he has been more vocal and bold in expressing his views.

Romney also has established – and his campaign has publicized – links with some of the country’s most high-profile hard-liners on immigration. They include Wilson, who pushed for strict measures against undocumented immigrants during his tenure as governor, and Kansas Secretary of State Kris Kobach, the author of some the most strict and controversial state-level immigration measures, including those that have become law in Arizona and Alabama.

“Latinos are well aware that Romney would be the most extreme presidential nominee of our time on immigration,” Acuna said. “Romney’s constantly on the wrong side of issues that matter to Latinos, and he’s embraced some of the biggest foes of our community. He’s threatened to veto the DREAM Act, which is supported by 85 percent of Latinos and promised to model a national immigration law based on Arizona’s discriminatory and inhumane policy. Latinos should be terrified of a Romney presidency.”

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On Monday, the Democratic National Committee held a media conference call to discuss Romney's immigration positions, and how harmful they would be for Latinos.

Senate Majority Leader Harry Reid, D-Nev., who took part in the call, said Republicans had exhibited “harshness, bitterness, meanness” in their discussions of immigration in an effort to pander to the Tea Party.

The Democrats assailed Romney for embracing the endorsements of proponents of strict immigration enforcement, and for saying that Arizona's tough immigration law could be a model for the nation.

“I can’t imagine Gov. Romney saying these things he has and these people running for president of the United States being proud of the Arizona law,” Reid said.

Neither of the other two GOP contenders, Gingrich or Paul, has made much of an effort in either Arizona or Michigan.

Romney, and his supporters, repeatedly have said the candidate is neither anti-Latino nor anti-immigrant. They categorically dismiss characterizations of him as unappealing to Latinos.

“These groups keep moving the goal post,” said Jose Fuentes, former attorney general of Puerto Rico -- who is co-chairman of Mr. Romney’s Hispanic steering committee – according to the Washington Times.

“Gov. Romney won Hispanics with more than 50 percent of the vote in Florida, where 15 percent of all voters were Hispanic. Not only that, but his message motivated a turnout 4 percent higher than expected or even the last presidential primary. His message is resonating. Democrats are overreaching here.”

A Republican presidential nominee would need to win at least 40 percent of the Latino vote in November, according to political experts.

This story contains material from The Associated Press.