EXCLUSIVE: Trump accuses Biden of lying about Obama's lack of endorsement

President TrumpDonald John TrumpCould Donald Trump and Boris Johnson be this generation's Reagan-Thatcher? Merkel backs Democratic congresswomen over Trump How China's currency manipulation cheats America on trade MORE on Monday accused former Vice President Joe BidenJoe BidenBiden leads, Warren and Sanders tied for second in new poll Analysis: Harris, Buttigieg and Trump lead among California donations The Hill's Morning Report: Trump walks back from 'send her back' chants MORE of lying about his lack of a 2020 endorsement from former President Obama in an exclusive on-camera interview with Hill.TV.

"How he doesn’t get President Obama to endorse him — there has to be some reason why he’s not endorsing him," Trump said outside the Oval Office. "He was the vice president. They seem to have gotten along. And how President Obama's not endorsing him is rather a big secret," Trump mused, adding, "Then he goes and lies and said, 'I asked the president not to endorse me.' Give me a break."

Trump argued Biden made the assertion because "he’s embarrassed by the fact that Obama’s not endorsing him, so he goes out and says, 'I asked President Obama not to endorse me.' ... So it could be that President Obama knows something, but there is something going on in that brain of his."

Pressed on what exactly is going on in Biden’s brain, Trump said, "I think he’s off. He’s different. We’ve all known him a long time. I’ve seen him for a long time. Frankly, he looks different, he sounds different, and he thinks different. Other than that, I hope he does very well."

Trump in a recent interview with "Fox & Friends" declined to endorse his own vice president, Mike PenceMichael (Mike) Richard PenceHow China's currency manipulation cheats America on trade Trump says he disagrees with 'send her back' chant Trump refers to Ocasio-Cortez as just 'Cortez' because it 'takes too much time' to say full name MORE, ahead of a possible run for president in 2024. Asked about his comments by NBC News's Chuck ToddCharles (Chuck) David ToddSanders campaign vents frustration with media, polls Megan Rapinoe reveals what she'd say to fans who are Trump supporters Rapinoe: Trump's message divides 'so he can conquer' MORE, Trump said he didn't answer because it was a "surprise question."

"I mean it's so far out. That would be the only reason. Now what happens in 2024 I don't know that Mike is going to run. I don't know who's running or anything else," the president said.