President Biden warned on Monday that the Supreme Court’s decision on presidential immunity meant that there were “virtually no limits on what the president can do” and urged voters to prevent former President Donald J. Trump from returning to the White House freed from the constraints of the law.

“The American people must decide if they want to entrust the president once again — the presidency — to Donald Trump,” Mr. Biden said during brief remarks, “knowing he’ll be more emboldened to do whatever he pleases whenever he wants to do it.”

Mr. Biden’s response to Monday’s court ruling was his first public remarks since he spent the weekend hunkered down with family at Camp David. His disastrous debate performance in Atlanta last week has led some Democrats to call for him to drop out of the presidential race because of concerns about his age and mental fitness.

The president appeared ruddier than he did during the 90-minute debate, when many observed that he looked very pale. He did not stumble over his words on Monday or falter midsentence. But he was using a teleprompter for the remarks, which lasted about four and a half minutes.

Mr. Biden also did not respond to several shouted questions at the end of the remarks on Monday, including one asking whether he intended to drop out of the race.

The Supreme Court ruled on Monday that Mr. Trump has significant immunity against prosecution on charges of trying to overturn the 2020 election. Mr. Biden called that a “dangerous precedent” that fundamentally alters the longstanding belief in the United States that no one should be above the law.