(CNN) -- President Joe Biden once called himself a "gaffe machine" -- and his latest slip-up is a whopper.

Speaking at the White House Conference on Hunger, Nutrition, and Health on Wednesday, Biden tried to acknowledge the presence of Rep. Jackie Walorski -- despite the fact that the Indiana Republican had died in a car accident in early August.

"Jackie, are you here? Where's Jackie? I think she wasn't going to be here -- to help make this a reality," Biden said.

The White House sought to play off the odd moment as nothing more than Walorski being "top of mind" for Biden.

"There will be a bill signing in her honor this coming Friday, so, of course, she was on his mind," said White House press secretary Karine Jean-Pierre. "She was top of mind for the President."

Which, sure. Everyone make mistakes.

But that's a pretty big mistake to make. And unfortunately for Biden, it plays into a caricature that Republicans -- led by former President Donald Trump -- have long been painting of him.

"This guy doesn't have a clue. He doesn't know where the hell he is," Trump said of Biden during the 2020 campaign. "This guy doesn't know he's alive."

At another point, Trump said: "Biden is shot. I'm telling you he's shot. There's something going on."

Biden's overall health didn't play much of a role in the 2020 election, however. Forty-one percent of voters in the 2020 election exit poll said that only Biden had the mental and physical health to serve as president. The same number -- 41% -- said that only Trump had the mental and physical stamina to do the job. Another 8% said neither did.

In 2021, amid the bungled US withdrawal from Afghanistan, Tennessee Republican Sen. Bill Hagerty suggested that the handling of the situation "created doubt not only in my mind, in the mind of many, many Americans, but also doubt in the minds of our allies" regarding Biden's ability to do the job.

Earlier this year, Kansas GOP Sen. Roger Marshall, a physician, suggested that Biden should submit to yearly cognitive testing. "I think we're all concerned for President Biden's mental health," Marshall said at the time. He added that he felt he had seen a "deterioration" in Biden's mental health over the past year.

Here's what we know for facts: Biden is 79 years old. He is the oldest person ever to be elected to a first term as president and, if he runs for a second term, will be the oldest person to do that too. His most recent physical was last November. At that time, the White House doctor said that Biden "remains fit for duty, and fully executes all of his responsibilities without any exemptions or accommodations."

What we also know is that Biden's age is an issue for voters well beyond the hardcore Republican base.

In a New York Times/Siena College poll conducted over the summer, Biden's age was a leading factor among Democratic voters who said they preferred the party nominate someone else for president in 2024.

As The New York Times noted in a July story on Biden's age, citing more than a dozen current and former senior officials and advisers:

"[T]hey acknowledged Mr. Biden looks older than just a few years ago, a political liability that cannot be solved by traditional White House stratagems like staff shake-ups or new communications plans. His energy level, while impressive for a man of his age, is not what it was, and some aides quietly watch out for him. He often shuffles when he walks, and aides worry he will trip on a wire. He stumbles over words during public events, and they hold their breath to see if he makes it to the end without a gaffe."

On Wednesday, Biden didn't make it to the end without a gaffe.

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