The long national nightmare that was Joe Biden’s presidency is over.

But the long political nightmare induced by Biden’s final act in Washington continues to divide Democrats.

“Original Sin,” Jake Tapper and Alex Thompson’s new tome about the former president’s ill-fated re-election campaign, has opened yet another fissure in a party full of them.

The book sheds further light on the conspiracy to pull the wool over voters’ eyes and saddle them with a half-functioning executive.

In the process, it indicts every major administration official who served under Biden by revealing that the president’s decline has been in progress since his 2020 campaign.

And that while they all but compared him to Superman, outsiders recognized his senility on sight.

Some Democrats are rightly outraged by their peers’ dishonesty — and ready to use it to their political advantage.

Antonio Villaraigosa, former Los Angeles mayor and current California gubernatorial candidate, has already turned his fire on two Biden alums: Xavier Becerra, who has announced his own campaign for the governor’s mansion, and Kamala Harris, who is choosing between that race and a third presidential bid.

“What did Kamala Harris and Xavier Becerra know, when did they know it, and most importantly, why didn’t either of them speak out?” Villaraigosa railed in a fiery statement last week.

Saying the two had “betrayed” their party, Villaraigosa argued their “cover-up” of Biden’s condition led “directly” to Trump’s election victory — and called on Harris and Becerra to “hold themselves accountable and apologize to the American people.”

Similarly, Dean Phillips, the former Minnesota congressman who mounted a much-maligned primary bid against Biden, has argued the Democrats can only redeem themselves by making “everyone that was aware of Biden’s condition . . . come clean.”

“No more evasions. No more insistence that he was sharp when you met him,” Phillips wrote at The Free Press.

“The whole truth will come out, and they would be wise to get ahead of it.”

Then he twisted the knife.

“If a relatively little-known congressman like me knew that Biden was incapable of leading the country in a second term, what does that say about the complicity of the real party bosses whose names we all know?” Phillips asked.

The two Dems’ rhetoric makes for an engrossing preview of a stark new dividing line within their party — one that’s sure to play a role in not just upcoming governors’ and Senate elections, but the 2028 contest to succeed Trump.

It’s between those who would paper over the Biden scandal or even deny it entirely, and those who believe it should politically disqualify all those complicit in it. 

And it won’t fade anytime soon: Early surveys of the 2028 Democratic primary field find Harris consistently on top, with former Transportation Secretary Pete Buttigieg finishing in the top three.

Both will be plagued by the lies they told in service of their old boss should they throw their hats in the ring.

Harris famously smeared Special Counsel Robert Hur for informing the American people that their commander-in-chief had wondered aloud if he was “still” vice president in 2009 — the very year he assumed the office for the first time.

And Buttigieg vouched for the president’s brain function by claiming he’d had to call in an Amtrak “expert” to handle Biden’s “detailed” questions about trains.

They’ll have a lot to answer for on the primary debate stage when their rivals ask why they misled the American people — not to mention what else they might be willing to lie about.

Senate Minority Leader Chuck Schumer, too, might face such questions should Rep. Alexandria Ocasio-Cortez choose to challenge him come 2028.

The Democrats’ internal reckoning over the Biden coverup is bound to be especially painful because it largely overlaps with existing cracks between the establishment and activist wings of the party.

Progressives in favor of adopting an even more unabashedly leftist agenda have long accused party elites of selling out their voters and their values in pursuit of power.

In turn, those elites have charged progressives with prioritizing ideological purity and factional goals over winning elections.

For the former group, the coverup reinforces the first narrative.

For the latter, continued recriminations against Biden and his team reinforce the second.

It’s said that time heals all wounds — but progressives in particular have an interest in keeping this one open and bleeding.

Cold, hard proof that party insiders were lying about the condition of the man with the nuclear codes is a visceral demonstration of the rot that leftists have long described.

It’s the kind of disgrace that can destroy presidential campaigns — and compel the sweeping, party-wide transformation they seek.

Isaac Schorr is a staff writer at Mediaite.