The most significant is obviously that the former president refused to cooperate with the National Archives and Justice Department until a search of his home was deemed necessary.

Meanwhile, Biden’s team has endeavored to highlight the fact they’ve been very cooperative, inviting various searches, including of his home last week — which revealed even more documents with classified markings, reportedly dating back to his days in the Senate.

That’s all fine. But there are two similarities that can’t be “messaged” away.

The first similarity has been widely discussed in the press and conceded by many of the president’s most ardent Democratic supporters: He had stuff he shouldn’t have had in places they didn’t belong.

Yes, Trump had more documents and possibly more sensitive ones. But the underlying misdeed is the same.

The second similarity has largely gone unnoticed, as the Daily Beast’s Matt Lewis has noted well. Very much like Trump, Joe Biden has a very difficult time admitting error.

Last week, Biden said he had “no regrets” regarding the classified document mess. Exactly one year earlier, he said, “I make no apologies” for how he pulled U.S. forces out of Afghanistan.

This was after he’d assured the public that the withdrawal would be secure and orderly.

”There’s going to be no circumstance where you see people being lifted off the roof of (an) embassy of the United States from Afghanistan,” he said. “It is not at all comparable (to Vietnam).”

On a human level, never mind as a matter of common sense, it’s impossible to believe that Biden had no regrets about Afghanistan or how this classified document mess has unfolded.

And as a political matter, this has been a fiasco. Does anyone believe he doesn’t wince every time he sees that “60 Minutes” clip of himself being shocked at Trump’s “irresponsible” handling of classified material?

Has the White House’s response really been flawless? On Jan. 12, White House spokeswoman Karine Jean-Pierre assured the public that “the search (for documents) is complete.” That was before more documents showed up in his home and garage.

Biden’s stubbornness is only part of the problem. No doubt lawyers and political advisers are reinforcing his instinct not give an inch to the press.

After the post-Afghanistan withdrawal press conference, Biden asked a friend how he did. The friend said “great.” Biden replied, “Yeah, but the press is going to kill me,” Biden said, “I’m f--- — no matter what I say.”

There’s also the larger political culture in which partisans believe any admission that bolsters the enemy is intolerable.

Indeed, Biden is hardly the first politician to struggle with admitting mistakes. Donald Trump took it to cartoonish extremes.

”I fully think apologizing is a great thing, but you have to be wrong ...,” he once said. “I will absolutely apologize sometime in the distant future if I’m ever wrong.”

I’ve long thought that Trump’s insistence that his infamous call with the president of Ukraine was “perfect” helped drive the effort to impeach him. Politically, claims of perfection enrage critics and proving imperfection is a lot easier than proving an admitted mistake was an impeachable outrage.

Therein lies Biden’s opportunity. As Lewis notes, “Biden was elected to be the opposite of Trump.”

That’s why Biden frequently falls back on one of his favorite folksy rhetorical refrains: promising to “always level with the American people and tell it to you straight.”

Biden would be much better off if followed his own advice — and I don’t just mean saying “mistakes were made.”

It would be much easier to argue that what he did isn’t as bad as what Trump did, if first he admitted his own missteps (and not for nothing: The legal standard isn’t “Is this worse than what Trump did?” but “does this violate the law?”).

Saying he has no regrets is not very different from saying what he did was perfect.

And Biden’s handwaving dismissal that “People know I take classified documents and classified information seriously” isn’t very far from Trump’s favorite lead-in for all kinds of groundless assertions: “Everybody knows...”

Either Biden is lying about telling it straight or he honestly believes he is. If it’s the latter, then he’s delusional.

I think there’s a deep hunger among voters for politicians to admit mistakes. Biden ran for office promising transparency, honesty, competence and normalcy. The way he’s handled this documents mess breaks all of those promises.