Biden Says He Is ‘Firmly Committed’ to Staying in the Race

President Biden on Monday dared his critics to “challenge me at the convention” if they want him out of the presidential race, refusing to step aside in a defiant letter to Democratic members of Congress and in fiery remarks on MSNBC’s “Morning Joe” program.

Declaring himself “frustrated with the elites” who have called for his exit from the race, Mr. Biden used the friendly venue of the morning news show to respond to demands that he demonstrate the kind of vigor that was missing from his listlessdebate performance on June 27.

Mr. Biden raised his voice repeatedly during the brief phone interview, including after one of the hosts asked him whether he had taken neurological exams after the debate. Sounding exasperated and angry, Mr. Biden rejected assertions that his stamina and mental abilities have not been tested in a real way.

“It drives me nuts, people talking about this,” he said.

Less than an hour before the interview, Mr. Biden’s campaign released a letter to congressional Democrats in which the president wrote that he was “firmly committed to staying in the race,” a pointed answer to allies on Capitol Hill who have been increasingly going public with calls for him to drop out.

“The question of how we move forward has been well aired for over a week now,” Mr. Biden wrote in the two-page letter, released by his campaign. “And it’s time for it to end. We have one job. And that is to beat Donald Trump.”

On “Morning Joe,” the president repeated his refusal to back down, saying he didn’t care about any of the high-ranking lawmakers or pundits who were calling for him to step aside, including Representative Jerrold Nadler of New York, the top Democrat on the Judiciary Committee, and Representative Seth Moulton, Democrat from