Jerrold Nadler

Jack Schlossberg, the grandson of John F. Kennedy, has built his campaign for a New York City House seat around turning the page on the Democrats’ old guard.

Yet when he debuts his first paid advertisement on Wednesday, the 33-year-old candidate has chosen his party’s oldest living leader, Representative Nancy Pelosi of California, to do the talking.

The choice reflects the unique challenge Mr. Schlossberg faces ahead of a marquee June primary against more seasoned rivals. He may have star power and youth, but he is still trying to persuade aging voters who form the Democratic base that he is serious and experienced enough to represent a storied Manhattan district — home to corporate chieftains, media empires and cultural meccas.

The 30-second ad, which was shared first with The New York Times, uses Ms. Pelosi, a former House speaker, to make his case. In it, the congresswoman, 86, speaks directly to the camera to say that Mr. Schlossberg has “a deep sense of duty” and the kind of energy that could help propel Democrats back to power nationally.

“This moment calls for leaders who understand the stakes and how to deliver for the people they serve,” she says, sometimes over clips of him campaigning. “Jack Schlossberg is that kind of leader.”

Mr. Schlossberg is among the first candidates in New York’s 12th District to start spending on paid media. But a handful of super PACs funded by competing A.I. companies and former Mayor Michael R. Bloomberg have already burned through millions of dollars trying to sway voters toward or away from his rivals.

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