Many Democratic primary voters consider 76-year-old former Vice President Joe Biden the most likely candidate to beat President Trump. But history shows that Democrats win presidential elections with younger, charismatic, "hope-and-change" nominees like John F. Kennedy or Barack Obama, not older, experienced ones like Hillary Clinton and John Kerry.

In three of the last seven presidential elections, Democrats won against Republican candidates more than 20 years their senior.

Bill Clinton was 46 in 1992 when he beat President George H.W. Bush, then 68. In 1996, Clinton won reelection at 50 against GOP nominee Bob Dole, then 73. At 47, President Barack Obama beat Sen. John McCain, R-Ariz., who was 72 during the 2008 election.

When those match-ups happened, "younger people [were] disproportionately more of the electorate than they normally are,” Democratic strategist Jeff Hewitt told the Washington Examiner. Even in other years, he noted, youth benefits a Democrat. “Any time it’s 10, 12 years [of an age difference] or more, I think it’s a generational shift that younger voters get excited about.”

Thor Hogan, professor of politics and environmental sustainability at Earlham College in Indiana, also noted the trend of younger Democrats winning presidential elections in a November 2018 analysis.

“In the last century, the [Democratic] party has never won with a non-incumbent who was older than 52,” Hogan wrote. “The youth of successful Democrats makes perfect sense. Democrats are the party of progress, of hope, and of change. It seems quite sensible, therefore, that their voters would gravitate toward youth, vigor, and new ways of thinking.”

Kennedy had charisma and a sense of youthful optimism going for him that 1960 opponent Richard Nixon, though just a few years older than Kennedy, lacked. Democrat Jimmy Carter in 1976 was 11 years younger than the Republican incumbent he defeated, Gerald Ford.

The diverse 23-candidate Democratic presidential field includes members of the aging Silent Generation such as Biden, 76, and Sen. Bernie Sanders, 77, older millennials, including South Bend, Ind., Mayor Pete Buttigieg, 37, Hawaii Rep. Tulsi Gabbard, 38, and California Rep. Eric Swalwell, 38, and plenty of Generation X-ers and Baby Boomers in between.

The generational-gap advantage that Hewitt mentioned would not apply to Biden or Sanders in a race against Trump, 72, but he thinks it would definitely boost Buttigieg, former Texas Rep. Beto O'Rourke, 46, or even New Jersey Sen. Cory Booker, 50. Booker "seems younger than he is," Hewitt said.

Sanders did dominate the youth vote in 2016 primaries, but "the younger electorate isn't nearly as fired up about Bernie Sanders this year," Hewitt said. "His policies seemed a lot more radical four years ago than they do now in comparison to the rest of the Democratic Party. I think with a lot of the Democratic party moving more left and more progressive, that negates some of the support he was going to get from younger voters.”

Attendees at presidential campaign events in New Hampshire and Iowa last month expressed their desire for a fresh presidential nominee .

“I’ve kind of been excited for looking for somebody new, like a new JFK, a New Frontier kind of thing,” Goffstown, N.H., resident Eric Emmerling, 63, told the Washington Examiner before seeing Biden speak in Manchester.

Emmerling, who manages a nonprofit organization, supported Sanders in 2016 but is not planning to do so this time around. “I kind of think you have your time, and you have an opportunity and you miss it, and I don’t know if the country is going to be really supportive of Biden or Sanders,” he said.

Retired Iowa Falls, Iowa resident Craig Harris, 71, would like to see a younger, female nominee. “I don’t want to go for somebody older that I am,” he said between attending events for Sen. Kirsten Gillibrand. D-N.Y., and Sen. Amy Klobuchar, D-Minn., over Memorial Day weekend.

Fairfield, Iowa, security worker Marc Krover, 34, attributed Buttigieg's rise in prominence to his age. "Younger generations maybe want to look towards more of a new, younger [candidate], maybe a more fresh viewpoint,” he said. Krover was attending a Booker event when he spoke.

A Gallup poll conducted in April suggests that aversion to older presidential candidates could be a factor in 2020: 63% of Americans said they would vote for someone over 70 years old, while 71% say that they would be willing to vote for a candidate younger than 40.

"If it's two old guys running, or two older candidates running, I think at that point, Democrats only win because of anti-Trump enthusiasm," Hewitt said. "A younger candidate has a much better chance."