Tim Ryan, a former Ohio congressman, called on Democrats to replace President Biden with Vice President Kamala Harris to lead the party’s ticket in the November election against former President Donald J. Trump.

Mr. Ryan, in a Newsweek opinion column, wrote that he had lost confidence in Mr. Biden’s ability to defeat his rival after watching the president struggle in Thursday’s head-to-head debate with Mr. Trump.

He noted that Mr. Biden had said he would be a bridge to a new generation of Democratic leaders, an idea he said he liked. “Regrettably, that bridge collapsed last week,” he wrote.

“Witnessing Joe Biden struggle was heartbreaking,” Mr. Ryan wrote of the debate. “And we must forge a new path forward.”

In 2020, Mr. Ryan endorsed Biden after his own bid for the party’s nomination failed. During the midterm elections in 2022, he lost his bid for Senate in Ohio to J.D. Vance, a Republican who is said to be on Mr. Trump’s shortlist of running mates.

Since Mr. Biden’s poor debate performance last week, the noise has intensified about whether Democrats should replace him as the party’s nominee. He is scheduled to accept the Democratic nomination at the party’s convention in August in Chicago.

While figures such as Gretchen Whitmer and Gavin Newsom, the governors of Michigan and California, have drawn attention as potential replacements, Mr. Ryan wrote that Ms. Harris gives Democrats their best shot at holding the presidency.

“Those who say that a Harris candidacy is a greater risk than the Joe Biden we saw the other night and will continue to see are not living in reality,” he wrote. “It is not just utterly preposterous for the haters to say that, it is insulting.”