Jerry Nadler was at it again Tuesday, waxing indignant about former White House counsel Don McGahn’s refusal to testify before the House Judiciary Committee. It’s all a show, meant to keep old news in the headlines, and to appease the large “Impeach Now!” wing of the Democratic Party without actually doing anything.

Everyone on Judiciary knows perfectly well that Congress can’t compel testimony from top presidential advisers except in the most extraordinary circumstances: The chief executive’s right to frank, confidential discussions with his staff is well-established.

So Nadler’s bluster about how he’ll “go to court to secure” McGahn’s appearance is just noise for the cameras.

Then again, that’s all the testimony itself would be — a public spectacle telling no one anything new. With full White House permission, McGahn cooperated fully with special counsel Robert Mueller’s investigation, and it’s all in Mueller’s report.

Mueller is also refusing to play along, saying he won’t testify publicly about anything except what’s in his report. Democrats claim they want Mueller’s input before deciding whether to start impeachment hearings, but they could get that in a closed hearing. How frustrating that he won’t serve the real agenda, which is to posture for the cameras.

The truth is that Mueller didn’t deliver what the Trump haters hoped for. Many House Democrats think they have enough to start impeachment now, but Nadler and Speaker Nancy Pelosi know that would be a disastrous waste of time.

Afraid to either impeach or drop the whole thing, Nadler & Co. are playing for time: demanding things they have no right to or need for so, they can suggest a new coverup is underway; regurgitating what’s already out there to give friendly media the excuse to relitigate it all and keep the hysteria alive.

Cowardly and cynical: That’s the Nadler show.