His comments on Thursday night came amid national and state-wide polls that showed the president trailing the Democratic presidential nominee, Mr Biden, at the ballot box.
One New York Times poll published this week put 14 points between Mr Biden and Mr Trump, who went on the attack against his Democratic opponent on Thursday.
“He doesn’t talk, nobody hears him. Whenever he does talk he can't put two sentences together,” Mr Trump told Fox News’ Sean Hannity. “I don’t want to be nice or unnice, okay?”
"I mean, the man can't speak. And he's going to be your president because some people don't love me, maybe”, he continued. “All I’m doing is doing my job”.
Mr Trump, who appeared to defend his administration’s actions on Covid-19, had seen Mr Biden attack him some 24 hours earlier as the American death toll passed 125,000.
The Democrat told supporters in Pennsylvania that Mr Trump has behaved “like a child” throughout the crisis.
“[Trump’s] like a child who can’t believe this has happened to him — all his whining and self-pity,” said Mr Biden. “Well, this pandemic didn’t happen to him. It happened to all of us.”
Mr Biden also denounced Trump administration attempts to overturn the Affordable Care Act, otherwise known as Obamacare, which has insured some 20 million Americans with health coverage during the current health crisis.
“If Donald Trump prevails in court, insurers would be allowed once again to strip away coverage, jack up premiums, simply because of the battle they survived fighting coronavirus”, said Mr Biden. “We need a public option, now more than ever”.