Representative Jerrold Nadler plans to step down as the top Democrat on the House Judiciary Committee next term, succumbing to calls for generational change as his party prepares to confront a second Trump administration.

Mr. Nadler, the 77-year-old dean of New York’s congressional delegation, had been facing a direct challenge from a close ally, Representative Jamie Raskin of Maryland. Mr. Raskin, 61, was said to have secured the votes necessary to defeat him.

The transition would represent a significant departure for House Democrats, who have traditionally awarded coveted committee leadership jobs based primarily on seniority. After November’s losses, though, many in the party have argued that President-elect Donald J. Trump’s return to power would require a younger, more dynamic crop of leaders.

Furious over being challenged, Mr. Nadler had initially fought to hold the position he has held since 2017. But on Wednesday, he conceded that he did not have a path to victory and endorsed Mr. Raskin to replace him in a letter to colleagues.

“As our country faces the return of Donald Trump, and the renewed threats to our democracy and our way of life that he represents, I am very confident that Jamie would ably lead the Judiciary Committee as we confront this growing danger,” Mr. Nadler wrote.

“Therefore,” he continued, “I have decided not to run for ranking member of the Judiciary Committee in the 119th Congress.”