But he never wavered from his central message: that President Trump was a danger to American values, while he was a stable, experienced leader who represented his party’s strongest option for the general election. Nor did he succumb to the purity tests on policy that coursed through the Democratic field during the 2020 primary season.

“A lot of smart Democratic strategists overcomplicated things,” said Elisabeth Smith, who was a top aide to Pete Buttigieg’s campaign, noting that most anti-Trump voters are animated chiefly by the burning desire to defeat him. Referring to Mr. Biden, she said, “Because of the way he conducted himself in primary, not kowtowing to every demand from the left, he never had to pivot from a primary to a general election message.”…

“Biden understood how much good will there still was for Obama,” said Ms. Smith, contrasting him with those Democrats who “were hitting Obama from the left.”

In the primary, Mr. Biden declined to join his competitors who called for decriminalizing the border and eliminating private health insurance, not wanting to give away his party’s advantage on two issues — immigration and health care — that lifted them to success in the 2018 midterms.