Multiple times each day, President Biden dials up Mike Donilon, a close adviser since the 1980s, to chew on the latest polls and headlines.

“What’s your instinct? What do you think?” Mr. Biden will ask Mr. Donilon, who recently left the White House for the campaign’s Delaware headquarters.

Once a week, Mr. Biden summons Ron Klain, his former chief of staff, to workshop the best attacks to use against former President Donald J. Trump as the presidential debate draws closer.

When he leaves for Delaware on weekends, Mr. Biden seeks out Ted Kaufman, a confidant who represents the president’s ties to the state that introduced him to the national stage more than a half-century ago.

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The three are at the center of the Biden world, part of an echo chamber where dissent is rare. In important moments, each has told the president news he did not want to hear, although not one of them said no when the president was considering whether to run for a second term. They are also decades older than the young voters who could decide the election, which worries many of the president’s allies.