Donald Trump must believe in the theory that if you say something often enough — regardless of its fallacy — that people will eventually believe it to be true.

I refer to “no collusion, no obstruction,” the mantra of the moment for the president of the United States.

I am running out of ways to say this, but I’ll try it yet again.

Special counsel Robert Mueller’s 22-month-long investigation into alleged “collusion” between the Trump campaign and Russians who hacked into our electoral system came up empty. Mueller didn’t find sufficient evidence of conspiracy to collude with the Russians. That particular case is closed.

I do get that. Honestly. I really do.

The obstruction matter is wide open. Mueller has said so. He said in his 448-page report, which Attorney General William Barr has let the world see, declares that Mueller’s team could not conclude that Trump and his campaign team did not obstruct justice; if they could have done so, they would have, Mueller said.

So, the obstruction issue remains an open — and quite inviting target — for Congress to pursue.

I’ve got some social media contacts who keep yapping at me because I won’t acknowledge that Mueller found no evidence of “obstruction.” One of those contacts actually is a friend of mine . . . who happens to be a Trumpkin. Hey, I still love my good buddy.

I regret, though, that he has bought into the Trump mantra of “no obstruction.”

To my dear friend and to others who happen to read these musings from me, I just need to reiterate for the umpteenth time: The case for obstruction of justice is far from being settled. Those 500 or so former federal prosecutors — who worked for Democratic and Republican administrations — all signed that letter that declared that had Trump not been president, he would have been indicted for obstruction of justice.

Let’s allow this matter to run its course.