Politico’s Emily Schultheis flags this video of four of Mitt Romney’s sons at a campaign event in Concord, New Hampshire. In it, Matt, second-eldest of the Romney brood, responds to a question about his father’s tax returns by cracking a birther joke at President Obama’s expense.

“He’s certainly not afraid of anything. He’s not hiding anything,” Matt Romney said in response to an query from an audience member on whether the former Massachusetts governor would release his tax returns. “You know, I heard someone suggest the other day that as soon as President Obama releases his grades and birth certificate and sort of a long list of things, then maybe he’d do it.”

Perhaps sensing trouble, the eldest Romney brother, Tagg, quickly jumped in.

“That was not my dad saying that,” he told the crowd.

“No, no, no, that was just a suggestion from someone else,” Matt Romney added.

Shortly after news of the episode circulated on the Internet, a new Twitter user, @Matt_Romney, appeared. And soon after, a tweet of apology.

“I repeated a dumb joke. My bad,” Matt Romney tweeted along with a link to the original Politico story.

While Romney’s sons appeared eager to brush off the statement, now it seems the Obama campaign is seizing on the incident.

“Mitt Romney’s son thinks President Obama should release his birth certificate. Guess he doesn’t have one of our mugs?” the Obama campaign tweeted Friday afternoon.

The tweet includes a link to the Obama campaign Web site, where users can purchase a $20 “Made In The USA” mug – the White House’s attempt to turn the birther issue into a little bit of campaign cash.