"I think he's the man that can carry the day," Brewer said on NBC's "Meet The Press," citing Romney's business background as well as his electability. "Mitt is by far the person that can go in and win."
Brewer joined Arizona Sen. John McCain and the state's other most prominent Republican leaders in backing Romney, who appears much stronger in Arizona than in Michigan, the other state voting Tuesday. Indeed, after debating in Mesa last Wednesday night, the candidates have camped out in Michigan, where Romney is locked in a close fight with former Pennsylvania Sen. Rick Santorum. They had no plans to return here before Tuesday's vote.
Brewer's endorsement was not unexpected. She told reporters Saturday she planned to make an announcement ahead of the primary. Speaking at the National Governors Assn. meeting in Washington, the governor said she had met with each of the GOP's four major White House hopefuls before the debate. She said she would have liked a more thorough discussion of illegal immigration during the event, noting that the candidates "are pretty much saying the same thing."
All have backed Arizona's tough border crackdown, though they have differed on how to deal with the millions of illegal immigrants already in the country.
Though the Romney campaign was quick to tout Brewer's endorsement, it carries some political risk. Her support could help Romney among conservatives -- particularly those concerned with illegal immigration. But it may play less well in the general election, when Latino voters will be an important swing group, especially across the Southwest.
Immigrant-rights groups and Latino activists criticized Romney earlier this month when he picked up the endorsement of former California Gov. Pete Wilson, a boogeyman in the Latino community for his backing of Proposition 187, a 1994 ballot measure targeting illegal immigrants.
Stephanie Cutter, a deputy campaign manager for President Obama, issued a taunting tweet on Saturday night.
"Gov. Brewer endorsement tomorrow?" she said. "Great for Republican primary, damaging to general election. Say goodbye to Hispanic vote."
With Sunday morning's announcement, Brewer joined a long list of Arizona Republicans backing the former Massachusetts governor, including every statewide elected official as well as the speaker and majority leader of the state House.
One of Romney's most prominent backers, Pinal County Sheriff Paul Babeu, stepped down last week as a co-chairman of Romney's Arizona campaign after allegations surfaced that he threatened his ex-boyfriend, a Mexican national, with deportation.
Babeu, who has gained prominence for his hard-line stance on immigration, vehemently denies the allegation.