Widespread concerns about President Joe Biden’s age pose a deepening threat to his reelection bid, with a majority of voters who supported him in 2020 now saying he is too old to lead the country effectively, according to a new poll by The New York Times and Siena College.

The survey pointed to a fundamental shift in how voters who backed Biden four years ago have come to see him. A striking 61% said they thought he was “just too old” to be an effective president.

A sizable share was even more worried: Nineteen percent of those who voted for Biden in 2020, and 13% of those who said they would back him in November, said the 81-year-old president’s age was such a problem that he was no longer capable of handling the job.

The misgivings about Biden’s age cut across generations, gender, race and education, underscoring the president’s failure to dispel both concerns within his own party and Republican attacks painting him as senile. Seventy-three percent of all registered voters said he was too old to be effective, and 45% expressed a belief that he could not do the job.

This unease, which has long surfaced in polls and in quiet conversations with Democratic officials, appears to be growing as Biden moves toward formally capturing his party’s nomination. The poll was conducted more than two weeks after scrutiny of his age intensified in early February, when a special counsel described him in a report as a “well-meaning, elderly man with a poor memory” and “diminished faculties in advancing age.”

Previous polling suggests that voters’ reservations about Biden’s age have grown over time. In six top battleground states surveyed in October, 55% of those who voted for him in 2020 said they believed he was too old to be an effective president, a sharp increase from the 16% of Democrats who shared that concern in a slightly different set of swing states in 2020.

Voters have not expressed the same anxieties about Donald Trump, who at 77 is just four years Biden’s junior. Their likely rematch would make them the oldest presidential nominees in history.

If reelected, Biden would beat his own record as the oldest sitting president, while Trump would be the second-oldest if he won. Trump would be 82 at the end of the term, and Biden would be 86.

In the most recent Times survey, 19% of all voters said Trump’s age was such a problem that he was not capable of handling the presidency. And in a sign of Republicans’ far greater confidence in their likely nominee, less than 1% of voters who backed Trump in 2020 said his age made him incapable.

Biden and his allies have rejected anxieties about his age and mental acuity as unfair and inaccurate. His campaign says its coalition will again rally around the president once it fully recognizes that Trump could win back the White House. It also argues that Biden faced age concerns in 2020 and still won.

Yet Biden is now four years older, and it may be impossible to completely reassure voters about his age given the inexorable march of time. The poll indicates that the worries about him are not only pernicious but also now intertwined with how many voters view him.