The Embattled Biden Campaign Tests Kamala Harris’s Strength vs. Trump

Under siege from fellow Democrats, President Biden’s campaign is quietly testing the strength of Vice President Kamala Harris against former President Donald J. Trump in a head-to-head survey of voters, as Mr. Biden fights for his political future with a high-stakes news conference on Thursday.

The survey, which is being conducted this week and was commissioned by the Biden campaign’s analytics team, is believed to be the first time since the debate that Mr. Biden’s aides have sought to measure how the vice president would fare at the top of the ticket. It was described by three people who are informed about it and insisted on anonymity because of the sensitive nature of the information. They did not specify why the survey was being conducted or what the campaign planned to do with the results.

The effort comes as some longtime aides and advisers to Mr. Biden are said to have become increasingly convinced that he will have to step aside from the campaign, and in recent days have been trying to come up with ways to persuade him that he should, The New York Times reported on Thursday. A growing number of prominent lawmakers have called for Mr. Biden to drop out or suggest he should reconsider his plans to run,

While some of Mr. Biden’s top aides have quietly argued that Ms. Harris could not win the election, donors and other outside supporters of the vice president believe she might be in a stronger position after the debate, and could be a more energetic communicator of the party’s message.

In memo to campaign staff on Thursday, Mr. Biden’s campaign chair, Jennifer O’Malley Dillon, and his campaign manager, Julie Chavez Rodriguez, wrote about the “path ahead.”

“In addition to what we believe is a clear pathway ahead for us,