Attorney General William Barr’s Sunday letter to Congress leaves no doubt: Three years of investigation, including two years under special counsel Robert Mueller, found no evidence of Team Trump “collusion” with Russia.

Yes, the news is a bit less definitive on the “obstruction” front: Barr says Mueller’s findings were “not sufficient to establish that the President committed an obstruction-of-justice offense,” but that basically boils down to the Washington establishment’s distaste for the way President Trump fired FBI chief Jim Comey, and raged against the Mueller probe as a “witch hunt.”

Crucially, Barr says that the president’s questionable actions “were not done with corrupt intent.” That is: Trump knew he hadn’t colluded, and acted accordingly toward those who seemed bent on suggesting otherwise to the American public.

Three years of intensive work by the nation’s best prosecutors and investigators resulted only in convicting Paul Manafort on crimes that had nothing to do with Trump or the 2016 campaign (and for skulduggery that also involved top Democratic lobbyists), plus a host of “process” charges (mostly lying to the FBI or Congress) against various peripheral Trump associates.

Oh, and indictments against a host of Russians for meddling in the 2016 campaign — but not in cooperation with Team Trump.

None of that — zero, zilch, nada — validates the years of breathless reporting about the investigations, nor (for example) the repeated claims of top House Intelligence Committee Democrat Adam Schiff that he had seen serious evidence of collusion.

For more than two years, America has been assured time and again that Mueller was onto clear evidence of Trump treason, more or less — and now it all stands exposed as wishful fantasies and outright lies.

Trump’s 2016 team did indeed sign up some pathetic third-raters, plus the sleazoid Manafort. The odious Roger Stone was a hanger-on, too.

But cleaner and better talent (especially from the GOP foreign and national security establishments) wouldn’t touch the long-shot populist campaign.

The Trump camp shouldn’t have hired Manafort or self-promoters like George Papadopolous. But none of them ever mattered.

The whole sorry affair shows at its core that Democrats just couldn’t and still can’t come to grips with 2016. They can’t believe Americans don’t think the way they do and so have to blame something, anything, for what went wrong.

But that doesn’t excuse all the supposedly neutral federal functionaries who seized on the “Steele dossier,” a Clinton campaign-funded hit produced by the smear merchants of FusionGPS to paint an utterly false picture of Trump treason, to launch the initial investigation.

Barr’s clear duty going forward (and that of FBI chief Christopher Wray) is to discover and expose every official in the Justice Department and the national security and intelligence bureaucracies who put partisan politics ahead of justice and the national interest — abusing key security powers such as Foreign Intelligence Surveillance Act warrants — to launch an investigation that now stands exposed as an obscene miscarriage of justice.