GRAND RAPIDS, Mich. - Back in his home state for the first time since November and facing a mounting challenge in the state by GOP rival Rick Santorum, Mitt Romney boasted of his Michigan roots Wednesday evening, pointing out old schoolmates before vowing to do what he says President Obama did not: Stand up to union bosses.

"I've taken on union bosses before, and I'm happy to take them on again, because I happen to believe that you can protect the interests of American taxpayers, and you can protect a great industry like automobiles without having to give in to the UAW, and I sure won't," said Romney.

Romney's pledge to confront the union bosses came in a response to remarks made Tuesday by United Auto Workers President Bob King, who said that Romney was "the last person who should be talking about the recovery of the U.S. auto industry."

King continued, "[W]hen we were at our darkest hour, Mitt Romney turned his back on the industry, their workers and the people of Michigan and in other places where Americans depend on the auto industry."

But tonight Romney pushed back against both King and Obama, whom, he quipped, "finally came around" to his idea of a managed bankruptcy for the auto companies.

"It has been a campaign by the president to foster the interests of organized labor. One example, of course, [is] here in Michigan. The president finally came around to my own view that Detroit needed to go through managed bankruptcy, the auto companies needed to go through managed bankruptcy to shed their excess costs," said Romney, who spoke at an office furniture warehouse. "And it took him six months to get there, but he got to the same place that I had suggested. But he gave the companies to the UAW when he was finished with the process. That, again, is something which I think is consistent with the fact that he got a lot of money from organized labor and felt that he should give them a favor."

The rally - dubbed a "welcome home rally" by the campaign - and an economic roundtable hosted by Romney, were the first campaign stops by the candidate since Santorum has seen a surge in the polls, mounting a credible threat to Romney in his home state.

Much of Romney's speech highlighted his history in the state, a dialogue the campaign has been pushing all week, releasing an ad entitled, "Growing Up," that featured Romney driving around Michigan talking about his childhood memories.

"I'm just delighted to be back in Michigan to see some old friends. Gosh, I got lots of old friends here. There's an old high school- We lived across the hall from each other," said Romney. "I see another, and a gal from high- There are a lot of high-schoolers here. I'm just- This really does bring back memories."

"I visited every county in Michigan, I think more than once, on my dad's campaign and my mom's campaign," said Romney, whose father, George Romney, served as governor of Michigan in the 1960s. "I've gone to the country fairs, so I didn't always see the best of each county but I saw - but I saw every county in this extraordinarily beautiful state. I love Michigan. I love the country."