As former president Barack Obama prepares to hit the campaign trail to boost Joe Biden’s bid for the White House, he lashed out at President Trump on Wednesday. In an interview on the liberal “Pod Save America” podcast, Obama particularly blasted his successor for continuing to spread misinformation.

“Trump is a symptom of [misinformation] and an accelerant to it,” Obama said. “When you look at insane conspiracy theories like QAnon seeping into the mainstream of the Republican Party, what that tells you is that there are no more guardrails within that media ecosystem.” (QAnon followers believe, baselessly, that Trump is battling a cabal of “deep state” saboteurs who worship Satan and traffic children for sex.)

The interview comes as Obama reportedly plots a swing through key battleground states like Florida and Wisconsin to make a closing argument for his former vice president less than three weeks before the election. It also represents the latest instance of him upping his rhetoric against Trump. Where Obama was once reluctant to verbally spar with the president, in recent months, he has issued dire warnings about Trump’s leadership in a fiery Democratic National Convention speech and slammed the president in campaign ads.

A theme of Obama’s interview was his frustration with Trump continuing to push unfounded conspiracy theories — and his anger at Republicans for not distancing themselves from those claims. Speaking with his former aides Jon Favreau and Tommy Vietor, Obama said he was dismayed that Republicans didn’t call out Trump last week for pressuring the Justice Department to go after him and Biden.

“The allegations are so absurd that even Republican-controlled committees looking into it have dismissed them. And Attorney General Barr has dismissed them,” Obama said. “I’m disappointed that Republicans who know better have not checked him on this.”

The Trump campaign did not respond to a request for comment.

Obama also took conservative media to task for increasing partisanship, arguing that the approach has benefited Trump at the detriment of his party.

“Trump is expressing or mirroring and, in some ways, explicitly exploiting and took on the crazy that was being pumped out through these venues each and every day,” the former president said. “If that stuff is still being pumped out and Trump goes away, someone else will meet that market demand. But on the other hand, do I think that is inevitably what the Republican Party has to be? No, I don’t think it does.”

Obama reflected on Trump’s first foray into mass conspiracy peddling — the false claim that Obama wasn’t born in the United States. The former president said he noticed in his research for his upcoming memoir, “A Promised Land,” that Trump was complimentary toward him during his first couple years in office, even going so far to say he was doing “a great job.”

But Obama said that changed when the birtherism conspiracy theory took off, launching the real estate mogul’s years-long effort to delegitimize the nation’s first Black president.

“The guy just decided he wanted attention, like whether it was to promote ‘Celebrity Apprentice’ or whatever, he sort of looked and saw what was being said,” Obama recalled Wednesday, “and he said, ‘Oh, if that’s what folks want, I can do that with even less inhibition. … I don’t need a dog whistle, I’m just gonna go ahead and say it.’”

Obama also took aim at Trump’s foreign policy, arguing that he lacks the patience and focus for the job.

“Over the last four years, it’s not as if Trump has been all that active internationally. I mean, the truth is he doesn’t have the patience and the focus to really substantially change a lot of U.S. foreign policy,” Obama said. “What he’s done is he’s systematically tried to decimate our entire foreign policy infrastructure.”