Mr Trump, who regularly calls his top Democratic presidential opponents "Sleepy Joe" and "Crazy Bernie" was asked whether he could deliver his message without the controversial rhetoric.
He told the event in Scranton, Pennsylvania and broadcast on Fox News: "You can't turn your cheek.
"When they hit us, we have to hit back. I really feel that."
The first question, from an undecided voter, was about the administration's response to the virus.
The number of the cases in the US stood at about 200 on Thursday, including 12 deaths - 11 in Washington state and one in California.
He said: "Everybody has to be calm. It's all going to work out.
"We hope it doesn't last too long."
It was Mr Trump's first 2020 visit to Pennsylvania, a battleground state he won by about 44,000 votes in 2016.
The state is home turf to former Vice President Joe Biden, who spent his first 10 years in Scranton before his family moved to Wilmington, Delaware.
Meanwhile, during a lightning round, Mr Trump, a self-proclaimed germaphobe, said he has gotten over his aversion to hand-shaking, even during the age of the coronavirus.
"You can't be a politician and not shake hands," the president said.
"The bottom line is I shake anybody's hand now. I'm proud of it."