He does retain obvious strengths as a potential candidate: He is still at the top of the polls, albeit not quite as high as he was at the start of the year. Democratic voters view him in overwhelmingly favorable terms, as a thoroughly qualified commander-in-chief and an emblem of the Obama administration. And there is also deep and lasting sympathy for Mr. Biden and his family after the death of his eldest son, Beau, from cancer in 2015.

Yet his decision to wait on announcing his candidacy has come with a cost, in part because he did not use the time to better prepare for some of the most inevitable questions about his lengthy record in politics. Without a campaign in place, Mr. Biden has also not done any polling to determine his most glaring liabilities or substantial assets.

Mr. Biden has yet to apologize to Anita Hill even though he said last month that he regrets that “he couldn’t give her the kind of hearing she deserved” — a reference that seemed to play down his powerful role as chairman of the Senate Judiciary Committee when Ms. Hill testified at Justice Clarence Thomas’s confirmation hearing in 1991 that he had sexually harassed her.

Mr. Biden has also done little to reach out to feminist leaders before entering a campaign in which his mixed record on abortion rights is sure to be an issue. He has not contacted Ilyse Hogue, the head of Naral Pro-Choice America, or Cecile Richards, the former head of Planned Parenthood, according to Democratic officials.

He has said publicly that he wants a campaign that reflects the country, but his inner circle remains largely white and male, and some of his overtures to next-generation Democratic strategists have fallen flat or petered out, several people briefed on the efforts said.

Karine Jean-Pierre, a top official with the liberal group MoveOn, met privately with Mr. Biden but elected not to pursue a campaign job. Biden advisers sought to hire Tara McGowan, a highly regarded Democratic digital strategist, and Emmy Ruiz, an operative who managed several Western states for Hillary Clinton in 2016. Neither signed on, and Ms. Ruiz now works for Senator Kamala Harris of California. (All three women declined to comment or did not respond to requests.)