With the news that Joe Biden is dropping out of the 2024 presidential race, Donald Trump‘s campaign is facing a new challenge: that the Republican — who has spent years criticizing Biden’s age — is now the oldest person in United States history to be nominated for president by a major party.

Biden, 81, has for years been subject to criticism about his perceived cognitive health, and polls have shown that a majority of voters had concerns about the president’s age even well before the 2024 campaign got underway.

But on Sunday, July 21, Biden dropped out of the presidential race in a historic move and promptly endorsed Vice President Kamala Harris, who is 59.

The news that Biden is no longer running means that the issue of age may now fall solely on 78-year-old Trump. Polls have long suggested that voters would prefer to see younger candidates on the general election ballot.

As the oldest president in U.S. history, Biden routinely heard concerns about his ability to serve an additional four years, which would have made him 86 at the time he left office. But in recent weeks — particularly in the wake of the first 2024 presidential debate — many of those concerns came from leaders in Biden’s own party.

Republicans and the Trump campaign have seized on those criticisms even as far back as the 2020 campaign, when Trump referred to Biden as “Sleepy Joe.” In more recent months, Trump has refrained from directly criticizing Biden’s age, though he has mocked the Democrat for his debate performance.

Trump responded to the news of Biden’s decision to withdraw from the race with a Truth Social post, in which he claimed the president “is certainly not fit to serve – And never was!”

“We will suffer greatly because of his presidency, but we will remedy the damage he has done very quickly,” Trump wrote elsewhere in the post.

Biden became the oldest person to be sworn in as president of the United States at his 2021 inaugural ceremony, when he was 78. Trump was previously the oldest-ever president to take office, and was 70 at his 2017 inauguration.

If elected to serve a second term, Trump will leave office when he’s 82 years and 7 months old. That would surpass Biden’s anticipated record of 82 years and 2 months old, again making Trump the oldest president in U.S. history.