Biden and Sanders aides told me they see the age of the other Democratic front-runner as largely neutralizing the age issue, even as internal worries persist that it could prove one of their biggest liabilities with voters. They believe Trump helps blunt the issue too: He still refuses to release his medical records, and he’s better known for live-tweeting Fox News than for the kind of marathon schedules that both Biden and Sanders like to keep up on the campaign trail.

But at least 18 Democrats running for president think voters want something fresh: not only someone younger, but someone who represents a whole new start—that’s the best way the party can contrast itself with Trump. Several candidates’ aides have quietly pushed an argument about Biden in particular that’s similar to his own old “dear old dad” attack.

Read: Joe Biden is running for president

Biden has made clear in private conversations with aides that he doesn’t like being seen as old, and that’s part of why he won’t engage in any suggestion that he should serve only one term.

“It’s a legitimate question to ask, about my age,” Biden said yesterday on The View, during his first interview of the race. “It’s a question of—hopefully with age comes wisdom, and experience—can things get better?” Responding directly to Trump’s swipe earlier in the day, he said, “If he looks young and vibrant compared to me, I should probably go home.”

For decades, the Democratic path to winning the White House has been about offering something new—from John F. Kennedy and Jimmy Carter to Bill Clinton and Barack Obama. Biden is counting on the power of nostalgia—of the Obama era, of a calmer time—to overcome that in this race, especially with Democrats nervous about winning and feeling exhausted from the past three years. Trump is already the oldest first-term president ever. Maybe the next one will be older.

An ad from joe biden’s 1972 senate campaign

Referring to Biden, former Pennsylvania Governor Ed Rendell told me, “He’s not running against a spring chicken” and “looks, like, 15 years younger than Trump.” And anyway, Rendell said, Biden is in the race “because of his character and his intelligence, not because of his youth.” Rendell is 75 years old himself. (Biden’s campaign declined to comment.)

The Democrat under 70 who’s currently doing the best, of course, is the youngest one: 37-year-old Pete Buttigieg, who’s less than half the age of Biden and Sanders. His whole campaign is centered on the idea that he’ll be alive long enough to experience the full consequences of decisions the next president makes. When asked at an appearance back home in South Bend, Indiana, on Monday why he thinks he’s currently polling third, Buttigieg argued that “there’s a lot of excitement around the idea of something completely different. And there’s a lot of energy for generational change.” When I pointed out that two candidates in their 70s, Sanders and Biden, are ahead of him in the polls, Buttigieg cited their high name ID as an explanation. “The thing that’s surprising us is that perhaps being one of the very least well known, we’ve been able to vault to the top tier—and I think the generational energy helps to explain that,” he said.