The president imitated Xi Jinping in remarks in Baltimore on Thursday.
"He's hard, oh boy … a mad guy, he wants Sleepy Joe, can you imagine those guys in a room?"
In an anti-environmental riff, he also blamed energy-efficient bulbs for giving him "orange air".
"The light is not good! I still look orange," he joked.
"And you too, the light is the worst."
Mr. Trump also returned to his familiar insult of Pocahontas, aimed at Elizabeth Warren.
"I thought she was gone! Now she seems to be able to beat Joe asleep," he said.
Joe Biden is still considered the Democratic favorite, but his lead in the ballot has declined in recent days.