President Donald Trump questioned former Vice President Joe Biden’s mental state on Monday.

“There is something going on in that brain of his,” Trump said in an interview with Hill.TV. “I think he’s off. He’s different. We’ve all known him a long time. I’ve seen him for a long time.”

Trump appears to have watched some of Biden’s appearances on the campaign trail as he currently leads the Democrat field.

“Frankly, he looks different, he sounds different, and he thinks different,” he said. “Other than that, I hope he does very well.”

The president questioned why former President Barack Obama failed to endorse his running mate.

“How he doesn’t get President Obama to endorse him — there has to be some reason why he’s not endorsing him,” Trump said. “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 accused Biden of lying about why Obama had not endorsed him.

“Then he goes and lies and said, ‘I asked the president not to endorse me,'” Trump said. “Give me a break.”