WASHINGTON — From his treatment of Anita Hill in the 1990s to his unwelcome hugs of women, from his recent flip-flop on abortion funding to his latest remarks about segregationists, Joseph R. Biden Jr. has spent the early months of his third presidential bid doing a lot of explaining, justifying and pushing back.

The one thing he hasn’t done is bow to critics and apologize outright.

“Apologize for what?” Mr. Biden snapped on Wednesday evening after Senator Cory Booker of New Jersey, a rival in the 2020 campaign, said he should express regret for citing two Southern segregationist senators as examples of civility in politics. “There’s not a racist bone in my body.”

A few hours later, after Mr. Booker responded angrily on CNN to the former vice president, Mr. Biden called him in an effort to decrease tensions, according to two people familiar with the call. The tone between the men was conciliatory; still, the former vice president and his allies have stood by his remarks.

For decades, Mr. Biden’s garrulous political style has led to the kind of gaffes that contributed to the demise of his previous presidential aspirations. Yet Donald J. Trump’s refusal to admit any misstep during his winning presidential campaign may have shifted the gaffe gauge in American politics — as well as some Democrats’ expectations about their own candidates.