COMMERCE, Mich. — In a speech to thousands of supporters at a family orchard outside Detroit Friday afternoon, Mitt Romney tried a joke as he touted his family roots in the state — and got himself in trouble in the process.

After he and Mrs. Romney both took turns talking about how excited they were to be "home" in Michigan, Romney said, "“Nobody ever has to see my birth certificate. They know this is the place where I was born and raised.”

The line, which prompted laughter and then cheers from the roughly 5,000 people gathered here, was an apparent reference to the long-debunked conspiracy theory that President Obama was born in Africa, and therefore not Constitutionally qualified to be president.

But the Romney campaign quickly pushed back against questions about whether Romney was invoking "birtherism."

"The governor has always said, and has repeatedly said, he believes the president was born here in the United States," said adviser Kevin Madden. "He was only referencing that Michigan, where he is campaigning today, is the state where he himself was born and raised."

A campaign aide told BuzzFeed, on condition of anonymity, that Romney did not plan the birth certificate joke in advance, and that it was an "off-the-cuff reference to him being a homegrown guy of Michigan" that was wrongly interpreted by the press.

Still, a spokesman for the Obama campaign seized on the opportunity to decry Romney for extremism.

“Throughout this campaign, Governor Romney has embraced the most strident voices in his party instead of standing up to them," said spokesman Ben LaBolt. "It’s one thing to give the stage in Tampa to Donald Trump, Sheriff Arpaio, and Kris Kobach. But Governor Romney’s decision to directly enlist himself in the birther movement should give pause to any rational voter across America.”

Meanwhile, the reaction from the crowd of Republicans here was largely enthusiastic, with some laughing it off as a politically incorrect joke, and others treating it as a welcome attack on what they believe to be the coverup of the president's birthplace.

Asked what he made of Romney's line, Jim Barzakov, a retiree from Berryville, MI, expressed frustration with reporters' fixation on the issue.

"What is it with this birth certificate? It's every question I get from you guys!" he said. "You must be all liberals! What kind of a question is that?"

He then said the meaning of the line was simple: "It says Romney has his birth certificate; Obama can't find his." Asked about the certificate the White House released last year, Barzakov dismissed it as a "photoshop certificate."

Therese Cayline, who works at a real estate management company in Waterford, MI, said she doesn't consider herself a "birther" — but raised several of the talking points espoused by skeptics of the president's birth certificate.

"[Romney] was born and raised in Michigan and as far as Obama goes, his grandma was there at his birth and his grandma has never been outside Kenya," Cayline said. "So I find it ironic that he won't show the real birth certificate."

But Laura Barnett, 22, from Wesfield, MI, said the birth certificate line was just a joke, not to be taken too seriously.

"I think people, if they want to make it controversial, they can," Barnett said. "But I think Romney was just being a little funny. I know the racism is serious and it's very controversial like I said but I think there's always room for some humor."