Republican gubernatorial candidate Mitt Romney on Wednesday picked former state GOP Chairwoman Kerry Murphy Healey to be his running mate.

"I want to offer the voters of Massachusetts the strongest, most broadest team that could possibly be available," Romney said.

In Massachusetts, governor and lieutenant governor are elected separately, but candidates who team up often campaign and advertise together. Republicans in Massachusetts have run joint tickets since 1990.

Romney, the former Salt Lake City Olympics chief, had insisted he would remain neutral in the lieutenant governor's race. But the other leading candidate for lieutenant governor — James Rappaport — is a wealthy, white businessmen just like Romney.

"From the Republican Party's point of view, they can't afford to have Jim Rappaport as lieutenant governor — they're mirror images of each other," Democratic state Rep. Michael Cahill said.

Rappaport vowed to fight on.

"He has endorsed her not because he likes her better but because she fits a perceived pairing," Rappaport said. "Mitt and I are going to disagree on a lot of things, and this is one of them."

On the Democratic side, state Treasurer Shannon O'Brien and millionaire businessman Christopher Gabrieli are running as a ticket. O'Brien is the only Democratic gubernatorial candidate to have chosen a running mate.