It was 90 minutes of chaos in a year of upheaval. But did it matter?

President Trump and Joseph R. Biden Jr. appeared onstage together for the first time on Tuesday. It was not exactly a debate.

Shouting, interruptions and often incoherent cross talk filled the air as Mr. Trump purposefully and repeatedly heckled and blurted over his rival and the moderator alike in a 90-minute melee that showcased the president’s sense of urgency to upend a race in which polls show him trailing.

ANALYSIS“An unpopular incumbent unfurling an often dubious defense.” Read our reporters’ analysis of the first presidential debate.
Mr. Biden labored to get his points in over Mr. Trump’s stream of interjections, turning directly to the camera for refuge from a scrum that hardly represented a contest of ideas. But Mr. Biden did not stumble, contradicting months of questions from the Trump campaign about his mental fitness, and Mr. Trump seemed to do little to bring over voters who were not already part of his base.

The impact on the race of the messy affair — given that 90 percent of voters say they are already decided — is an open question.

Here are six takeaways from the first debate.

Trump trampled over everything.

From the opening bell, Mr. Trump came out as an aggressor, speaking over Mr. Biden in what seemed to be almost din-by-design: Pull the former vice president, who has run as a statesman promising to restore the soul of America, into a mud-slinging contest.