As you may have heard, Thursday night was the first debate between President Biden and former president Donald J. Trump. In short, it was not a great night for Mr. Biden.

The president’s debate performance triggered significant panic among top Democrats, who for months have been dismissing concerns about Mr. Biden’s age.

So, how is this happening? Despite all the concerns polls showed about age, how has the Democratic Party arrived at this moment?

That’s a line of inquiry The Run-Up has been putting to senior Democratic leaders for the past 18 months. And we wanted to revisit some of those conversations now in a special episode.

They include selections of our interviews with Vice President Harris, former Housing and Urban Development Secretary Julián Castro, Democratic National Committee chair Jaime Harrison and Ron Klain, Mr. Biden’s former White House chief of staff.

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