In a new ad airing in Michigan, former Massachusetts governor Mitt Romney continues his recent focus on his own family history in Michigan.

The ad is more evidence that Michigan is the most important of the three contests on Feb. 28, when Arizona and Washington also vote. A pro-Romney super PAC has put $600,000 into Michigan ads.

Romney’s roots in Michigan mean a loss here to former Pennsylvania senator Rick Santorum — who has performed better in the Midwest and with blue-collar workers — would be embarrassing.

But Romney has been struggling in Michigan polls.

“Now when I grew up in Michigan it was exciting to be here,” Romney says in the new spot, “Growing Up,” as vintage footage of Detroit and a young Romney flicker across the screen. “Remember going to the Detroit Auto Show with my dad. That was a big deal.”

The candidate’s father, George Romney, was an American Motors executive before he became governor. A photo of the two together appears in the ad.

The spot then pivots toward a critique of President Obama, suggesting he is responsible for the auto industry’s decline.

“How in the world did an industry and its leaders and its unions get in such a fix that they lost jobs, that they lost their future? President Obama did all these things that liberals have wanted to do for years,” Romney says as he drives around the city in a Chrysler. “I want to make Michigan stronger and better. Michigan has been my home, and this is personal.”

His 2008 New York Times op-ed entitled “Let Detroit Go Bankrupt” is probably Romney’s biggest albatross in the Rust Belt state. He argued that a government bailout would kill the auto industry; the bailout happened and the car companies have rebounded.

The ad follows an op-ed in the Detroit News in which Romney defended his opposition to the auto bailout. There too, he emphasized his ties to the state.