President Joe Biden, 81, ended his 2024 re-election bid amid concerns about his increased vitality within the Democratic Party.

“There are cognitive issues,” former Sen. Bob Kerry, D-Neb., said in an interview with CNBC in July.

The issue of aging US lawmakers extends far beyond the presidency. At the start of the 118th Congress, the median age in the Senate and House of Representatives was 64 and 57, respectively, according to researchers at FiscalNote.

“The age of our politicians is kind of baked into the preferences of our voters,” said Christian Fong, assistant professor of political science at the University of Michigan. “They want someone who is successful in another job, first as a soldier, or as a businessman, or as a farmer. And then they want them to bring that experience and perspective to Washington.”

US national lawmakers are among the world’s oldest, according to a 2022 Stanford University study. The median age of the US population — 38.9 years in 2022 — is older than it’s ever been, according to Population Reference Bureau. The age of the typical registered voter was 50 in 2019, up from 44 in 1996, according to a Pew Research study.

Older voters tend to favor Republican politicians, while younger generations typically have a preference for Democrats. As said, Democratic Party legislators are, on average, slightly older than their Republican counterparts.

“It doesn’t have to be generational warfare or anything like that. But it really matters to representation in terms of the quality of the legislation that’s going to come out of Congress,” said Charles Hunt, assistant professor of political science at Boise State University.

President Biden’s endorsement of Vice President Kamala Harris, 59, led to a boom in Democratic Party donations. Earlier in July, former president Donald Trump, 78, was elected JD Vance, 39 years oldto be his running mate, a signal that a new generation of leaders could be moving up the ranks in Washington.

Watch video above to learn how senior politicians cling to power in Washington.