Harris Ad Features Obama’s Oblique Joke About Trump

Vice President Kamala Harris’s campaign is running a trolling ad ahead of the debate Tuesday directed at exactly one person: former President Donald J. Trump.

The ad highlights former President Barack Obama’s mocking comment in his speech last month at the Democratic National Convention in Chicago, referring to Mr. Trump’s “weird obsession with crowd sizes,” and an accompanying hand gesture. Mr. Obama brought his palms apart and then close together and glanced down at them meaningfully.

If Mr. Obama’s words and gesture retained some marginal degree of subtlety, the ad turned them into a sledgehammer, zooming in on his hands and his glance downward. Later, it showed empty seats against the sound of crickets and zoomed in on Mr. Trump’s hand — recalling Senator Marco Rubio’s jabs from the 2016 Republican primary in which he said Mr. Trump had small hands.

Those taunts prompted Mr. Trump, in a debate in 2016, to say: “He referred to my hands, if they’re small, something else must be small. I guarantee you there’s no problem.”

The Harris campaign seemed to dispel any doubt that the ad was intended more for Mr. Trump’s eyes than for voters, by noting that it was airing on Fox News in Mr. Trump’s home media market, West Palm Beach, Fla., and in Philadelphia, where he will be on Tuesday for the debate.

The campaign’s Instagram account posted the ad — which ended by cutting from scenes showing sparse attendance at Trump rallies to footage of a roaring crowd for Ms. Harris — with the text, “We’re running this ad on Fox News this morning for no particular reason,” and an emoji of an angelic, smiling face with a halo.

The campaign also said it had bought billboards in Philadelphia for ads focused on crowd size. One ad includes a