This afternoon, Donald Trump reminded the nation why he’s a dangerous surrogate for any political candidate.

Hours before hosting former Massachusetts governor Mitt Romney for a Las Vegas fundraiser, Trump appeared on CNN and repeatedly raised questions about President Obama’s place of birth.

Obama’s campaign has been making hay out of Romney’s appearance with Trump, and the celebrity mogul only gave Democrats more fodder in the contentious interview. After criticizing CNN for focusing on the “birther” issue, Trump repeatedly argued that Obama’s origins are unclear.

Video via BuzzFeed:

“Obama does not like the issue of where he was born,” Trump said. “He does not like that issue because it’s hitting very close to home. You know it, and he knows it.” He claimed Obama’s campaign was using “reverse psychology” to make reporters think that birtherism was bad for Republicans.

When host Wolf Blitzer pointed out that, in part thanks to Trump himself, Obama released his long-form birth certificate in 2011, the mogul replied, “A lot of people don’t agree with this birth certificate, a lot of people don’t think it’s authentic.”

Blitzer suggested that Trump was “beginning to sound a little ridiculous.” Trump shot back, “I think you sound ridiculous.”

For good measure, Trump also continued his insults of Washington Post conservative columnist George Will, who on Sunday called the mogul a “bloviating ignoramus.”

Will, Trump said, “is not somebody that I’ve respected. I don’t think he’s a very smart person.” He added, for good measure, “He was at Mar-a-Lago years ago and totally bombed.”

This kind of bomb-throwing is why Trump gets headlines — and why he endeared himself to many conservatives in his flirtation with a presidential run. But right now, Romney doesn’t need to be associated with this kind of sideshow.