But his numbers in 2020 have taken a dip.
The final meeting on Thursday between Mr. Trump and his Democratic opponent, Joseph R. Biden Jr., had the smallest audience of the five general-election debates that Mr. Trump has participated in. Roughly 63 million people tuned in live, a drop of about 10.1 million from the candidates’ opening debate last month.
In the pantheon of televised debates, Thursday’s edition did not make the Top 10.
The matchup in Nashville, which featured a relatively subdued president trying to revive a flagging candidacy, ranked 17th on the debate ratings chart since 1976, when Nielsen began measuring total viewership numbers for the events. It narrowly beat the 62.7 million who watched the final debate between Jimmy Carter and Gerald Ford in 1976, 44 years ago to the day from Thursday’s debate.
The ratings drop on Thursday could stem from many causes: viewer backlash to the raucous first Biden-Trump debate, competition from an N.F.L. game, or attrition from a marathon-length presidential race nearing the finish line. (The first debate of the Democratic primary took place in June 2019.)
Still, Mr. Trump is coming off another somewhat ominous ratings milestone: his unexpected Nielsen defeat last week to Mr. Biden in a battle of dueling network town-hall-style events. Mr. Trump lost in the ratings although his event was shown on NBC, CNBC and MSNBC, while Mr. Biden’s appeared only on the ABC network.
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Thursday’s event in Nashville amounted to the president’s final chance to make his case for re-election before a mass audience. Last week’s town-hall events attracted only 28 million viewers, and another debate, scheduled earlier this month for Miami, was called off after Mr. Trump objected to its virtual format.
Fox News drew the largest audience of any network on Thursday with 15.4 million viewers; the cable channel won the ratings race for the first Biden-Trump debate, as well. ABC and NBC — which aired prime-time coverage before the debate’s 9 p.m. Eastern start time — came in second and third among the networks, with 11.2 million and 10.6 million viewers, respectively.
The Nielsen data released on Friday included people who streamed the debate on their television screens, but not those who watched it solely on digital devices. There are still no widely accepted rating measures for the full digital audience.
The Nashville debate featured a newfangled microphone-muting scheme and a reined-in Mr. Trump, who took a calmer approach after his much-criticized performance against Mr. Biden last month. The moderator, Kristen Welker of NBC News, earned praise for her poised and firm approach to keeping the conversation running in an orderly fashion.
It was not long ago that Mr. Trump set audience records any time he stepped onto a debate stage.
His debut in a Republican primary debate, on Fox News in August 2015, still stands as the highest-rated nonsporting event in cable broadcast history, with an audience of 24 million viewers.
His first debate with Mrs. Clinton in 2016 drew 84 million viewers, setting a presidential forum record and beating the 80 million mark for Ronald Reagan’s sole debate against Jimmy Carter in 1980.
Even Mr. Trump’s chaotic battle with Mr. Biden last month notched 73.1 million viewers, making it the third-most-viewed presidential debate. Mr. Trump’s final matchup with Mrs. Clinton in 2016 had 71.6 million viewers, the fourth-highest total.
Ratings for late-campaign debates tend to bounce around. The third and final debate between Mr. Trump and Mrs. Clinton drew more viewers than their second, but fewer than their first. The third debate between Barack Obama and Mitt Romney in 2012 was the least viewed of that cycle.
In the campaign years of 1984 and 1988 — when only two presidential debates were held — the final debates attracted the biggest audience.