President Biden said in a prime-time Oval Office address on Sunday that the nation needed to “lower the temperature in our politics,” saying that he deplored the attempted assassination of former President Donald J. Trump and feared for the direction of the country’s politics.

“We cannot, we must not, go down this road in America,” he said, using the backdrop of the office for only the third time in his presidency. “There is no place in America for this kind of violence, for any violence, ever. Period. No exceptions. We can’t allow this violence to be normalized.”

“The power to change America,” he said, “should always rest in the hands of the people, not in the hands of a would-be assassin.”

The president’s six-minute speech — delivered from behind the Resolute Desk, which has been used by almost every president since Rutherford B. Hayes in 1880 — came just a day before Mr. Trump is set to attend his party’s nominating convention in Milwaukee. Republicans said the convention would proceed as planned, and Mr. Trump flew to Milwaukee on Sunday afternoon, vowing to remain “defiant in the face of wickedness.”

In his short speech, Mr. Biden said he would continue making his case for another four-year term, ignoring the calls from some in his own party to step aside. He said he expected Mr. Trump and his allies to attack his record during the convention, but he urged Americans in both parties to step back from a politics of hate and division that leads to violence.

“We debate and disagree,” he said. “We compare and contrast the character of the candidates, the records, the issues, the agenda, the vision for America. But in America, we resolve our differences at the ballot box.”