Attorney General William Barr is absolutely right to look into how the Russia probe got started.

The AG told lawmakers this week that he plans to review both “the genesis” of the investigation and “the conduct of intelligence activities directed at the Trump campaign.”

He was blunt: “I think spying did occur,” but he needs to see if it was justified.

That outraged Trump haters. Barr is “going off the rails,” huffed House Speaker Nancy Pelosi. “I was very disappointed,” whined ex-CIA Director John Brennan.

How rich. As the prez’s detractors themselves asked of the Russia probe, why fear a review if no one did anything wrong?

Let’s face it: Sufficient evidence of collusion to warrant a freewheeling, two-year probe by a special counsel — one that dogged the president and split the nation — has never emerged. So why was it launched in the first place?

Barr isn’t faulting the FBI rank-and-file but believes “there was probably a failure among a group of leaders there at the upper echelon.”

It’s a reasonable suspicion: Officials knew the Steele dossier was bogus yet still used it to get surveillance warrants. And what was the exact role of Justice Department biggie Bruce Ohr, whose wife worked for the dossier producers at FusionGPS?

Lest anyone doubt how far-reaching Mueller’s probe was, on Thursday a lawyer who worked in the Obama and Clinton administrations, Greg Craig, was indicted on charges stemming from it.

Specifically, he’s charged with making false and misleading statements about his work for a pro-Russian Ukrainian president. Paul Manafort’s crimes centered on similar work, making it plain that the sleaze Mueller uncovered was bipartisan — even as none of it involved collusion.

The nation deserves clear answers for why top law enforcement officials seemingly led the public to believe otherwise.