Donald J. Trump Sr. is the king of flip-flops.

He once supported Hillary Clinton; now he’s her arch-enemy. He once said states should determine pot use legality; now he’s all for the feds’ ruling the matter. Trump once said he’d cooperate “100 percent” with special counsel Robert Mueller …

Now he’s saying some quite different.

The president who in June 2017 said he would submit to interviews over the “Russia thing” now believes there’s no need for such an interview and implies he won’t agree to a request from Mueller for a sit-down visit.

Mueller, though, does have subpoena power. He can order the president to talk to him. The president then can determine whether he wants to disobey a lawful order. If he does, then he becomes a lawbreaker — kind of like the time President Clinton lied to a federal grand jury about his relationship with Monica Lewinsky; that lie handed congressional Republicans the pretext they were looking for, so they impeached the president.

Trump kept repeating himself this week about there being “no collusion” with Russians seeking to influence the 2016 presidential election outcome. He said it’s been “proven” there’s no collusion.

Actually, Mr. President, nothing has been proven. There’s no proof that the Trump campaign did work in cahoots with the Russians, or it didn’t. That is what Mueller and his legal team are trying to ascertain.

So … talk to the special counsel, Mr. President. You’ve got nothing to hide? Say it directly to Robert Mueller.