Mr Trump told an audience in Pennsylvania that Mr Biden would “appease … domestic terrorists” while he will “arrest them and prosecute them”.
His words follow the administration’s hard line approach to mass demonstrations against racial injustice which have taken place across the country in recent months.
The rally came the same day that Mr Biden paid a visit to Kenosha, Wisconsin, amid turmoil following the police shooting of Jacob Blake, a black man, seven times.
Mr Trump mocked Mr Biden for visiting two days after he had, claiming: “There was nobody there. He was a little late. I was going to say, ‘Hey listen, we ended that problem.’”
Mr Trump’s campaign believes its efforts to paint his Democratic rival as weak on crime will help him win back suburban voters, and especially women, who supported him in 2016 but have since soured on him.
The president was speaking in front of a crowd of hundreds packed into an airport hangar, where people stood closely together and few were seen wearing masks, despite the ongoing pandemic which has now killed more than 185,000 people and infected more than six million nationwide.
Pennsylvania currently restricts indoor gatherings to 25 people and outdoor events to 250 to prevent the spread of coronavirus.
But Mr Trump has been flouting both local restrictions and his own administration’s social distancing guidelines as he insists on campaigning in front of large crowds and tries to project the image that the virus is waning as he pushes to reopen the economy.
Mr Trump told the crowd that he is “all for” wearing masks, and urged them to be careful during the upcoming Labour Day weekend.
But at the same time, Mr Trump, who has rarely worn a mask, mocked Mr Biden for wearing one so often.
“Did you ever see a man who likes a mask as much as him?” he asked, proclaiming that “it gives him a feeling of security”.
“If I were a psychiatrist, right, you know I’d say, ‘This guy’s got some big issues.’ Hanging down. Hanging down,” he said.
