Jill Biden, in message to supporters, calls out special counsel's mention of Beau Biden's death

First lady Jill Biden on Saturday offered her first public defense of President Joe Biden's age and mental acuity since special counsel Robert Hur detailed what Hur said were notable lapses in the president's memory, spurring more scrutiny of his age and stamina.

In a fundraising appeal to supporters, Jill Biden slammed Hur's report, released on Thursday, as "inaccurate and personal political attacks," focusing on Hur's assertion that Joe Biden could not remember "within several years" when his son Beau died.

Although Hur's report said Joe Biden "willfully retained" classified documents while out office -- which the president disputes -- Hur could not recommend bringing charges because, he wrote, the "evidence does not establish Mr. Biden's guilt beyond a reasonable doubt."

"At trial, Mr. Biden would likely present himself to a jury, as he did during our interview of him, as a sympathetic, well-meaning, elderly man with a poor memory," Hur wrote.

Jill Biden fired back this weekend.

"Believe me, like anyone who has lost a child, Beau and his death never leave him," she wrote in the donor email. "I hope you can imagine how it felt to read that attack -- not just as Joe's wife, but as Beau's mother."

Like Joe Biden has, Jill Biden also invoked potential partisanship. Joe Biden called Hur a "Republican counsel," alluding to his background as a U.S. attorney in the Trump administration. (A spokesperson for Hur previously declined to comment to ABC News on the president reacting to the report.)

"We should give everyone grace, and I can't imagine someone would try to use our son's death to score political points," Jill Biden wrote in the email on Saturday. "If you've experienced a loss like that, you know that you don't measure it in years -- you measure it in grief."

The day Beau Biden died of brain cancer, on May 30, 2015, "is a day forever etched on our hearts. It shattered me, it shattered our family," the first lady wrote.

She also addressed the president's age head on, insisting that "Joe is 81, that's true, but he's 81 doing more in an hour than most people do in a day."

In a new ABC News/Ipsos poll released on Sunday, 86% of Americans said they think the president is too old to serve a second term, while 62% think the same of rival Donald Trump, who is 77.

During a hastily organized event on Thursday night during which Joe Biden defended himself against special counsel Hur's report, the president also mistakenly referred to the Egyptian president as the president of Mexico.

"He [Biden] had a 12-minute press conference where he was focused, engaged, purposeful, and all you're focused on is that one minute at the end," Democratic Sen. Chris Coons, a key ally, said ABC's "This Week" on Sunday.. "That's not what distinguishes him from his opponents."

Egyptian American Ahmed Ceif told ABC News at a Trump rally in Conway, South Carolina, on Saturday that former President Trump is sharper than Joe Biden's "fading" memory.

"You got to be more aware of what's going on," Ceif said. "You can't just let the person who's running the strongest country in the world be in that situation where he doesn't know which president is which."

Coco Farrow, a 19-year-old student at Coastal Carolina University, told ABC News at that same rally that with Joe Biden's age comes "experience."

"There's a lot to say about both sides. But I think it's about the experience that each person brings to the table and the time that they've spent in office," Farrow said.

Republican 2024 candidate Nikki Haley, who is running against Trump for their party's nomination, spoke bluntly of Joe Biden's issues.

"I wish Joe Biden well, I really do. But the Democrats, in the best interests of their party in our country, they need to find a new nominee," she contended in an interview with ABC News' Alex Presha on Sunday.

"I mean, look, you can watch the news and see, everybody's very worried at this point. Everybody's concerned," Haley said.

But just as the president and his aides -- both on the campaign and at the White House -- have argued, the first lady wrote on Saturday that "his age, with his experience and expertise, is an incredible asset and he proves it every day."

"Joe is the most resilient person I've ever known," she wrote. "When he gets knocked down, he gets back up and gets back to work. That's what he's doing."

ABC News' Hannah Demissie, Jeremy Edwards, Nicholas Kerr and Alexander Mallin contributed to this report.