A significant majority of Americans say they believe President Biden's mental fitness is a real concern they have about his ability to be president, according to the latest NPR/PBS NewsHour/Marist poll.

Respondents said so by a 62%-to-36% margin, rather than dismissing it as simply being a campaign strategy used by his opponents. Biden did, however, actually see a slight increase in his approval rating to 45%, up 4 points from last month. That indicates there will likely be a significant number of people who believe there are serious concerns about Biden's mental fitness but will vote for him anyway.

When it comes to former President Trump, who is also running again, 51% also said his mental fitness is a real concern, 43% said it was not.

Biden at 80 is the oldest president in U.S. history. He's been the subject of relentless accusations from the right about his acuity, but his age has also been a worry of Democrats, concerned about whether Biden gives them the best chance to win in 2024, especially if it's Trump as the GOP nominee again.

Almost 4 in 10 Democrats said his mental fitness was a real concern as did 7 in 10 independents and, as expected, more than 8 in 10 Republicans. Several key Democratic and swing groups saw Biden's mental fitness as a real concern, including those 45 or younger (69%), GenZ/Millennials (67%), men (66%), those without college degrees (66%), non-whites (64%) and those who live in the suburbs (63%), for example.

It's a serious vulnerability that will have Democrats biting their nails as the campaign heats up and holding their breath with each speech, news conference and debate.

Trump, who will be 78 on Election Day in 2024, would be five years older than Ronald Reagan was at his second inauguration. But beyond Trump's age, many have concerns about his temperament, persistent lies and, at times, bigoted speech.

Almost 8 in 10 Democrats but only one-fifth of Republicans said Trump's mental fitness is a real concern. A plurality (48%) of independents also said so but far fewer than said the same of Biden.

Trump's biggest problems continue to be with white, college-educated women and women who live in the suburbs and small cities.

Plurality thinks COVID emergency should have ended sooner

The COVID-19 national public health emergency ended on May 11th, but by a plurality, respondents in the survey said it should have ended sooner – 43% said so, 36% said it ended at the right time and another 1 in 5 said it happened too soon.

Republicans (68%) and independents (50%) in particular thought it should have ended sooner, while a majority of Democrats (54%) said it was the right time.

More than a quarter of Democrats, though, think it happened too soon, while just 1 in 10 Republicans and independents said so, another piece of evidence of the country's long divide over COVID and how to handle the pandemic.

The survey of 1,286 adults was conducted from May 15-18 with live interviewers using mixed modalities – by phone, cell phone and landlines, text and online. The poll has a margin of error of +/- 3.4 percentage points, meaning results could be about 3 points higher or lower than reported.