Democrats must have learned from the disastrous public hearings they’ve held in their attempt to impeach President Trump: Now, apparently, their witnesses must audition first behind closed doors before they go live before the TV cameras.

That was the case with the Dems’ “star” witnesses, US Chargé d’Affaires for Ukraine Bill Taylor and Deputy Assistant Secretary of State George Kent, who testified behind closed doors before appearing for Wednesday’s televised impeachment show. And for former US Ambassador to Ukraine Marie Yovanovitch, who debuts on the small screen Friday.

It’s also the case for David Holmes, the diplomatic staffer said to have overheard a phone call in which Trump said something supposedly incriminating. He’s scheduled to testify publicly next week.

Clever: By having witnesses go through closed-door hearings first, Dems can get a sense of what witnesses have to say privately and then tailor their questions for maximum impact during the public spectacle. The whole show can be stage-managed in advance.

And if a witness “fails” the private audition, heck, maybe they don’t even have him or her appear publicly at all.

In the case of Hunter Biden, Dems don’t even need him to testify privately: They already know he won’t help their cause. That’s thanks to his blatant conflict of interest involving his $50,000-a-month position with Ukrainian energy company Burisma while his dad, Joe Biden, was vice president — the very issue at the heart of Trump’s supposedly problematic phone calls. So they just won’t have him testify at all, privately or publicly.

The tryout process follows spectacular backfires during earlier Dem hearings that were supposed to sway public opinion toward impeaching the president but only made Democrats look foolish. Trouble is, even rehearsals don’t seem to help: The Taylor-Kent show turned out to be a huge bore-a-thon, failing to produce any firsthand evidence to warrant impeaching the president.

What a farce. Democrats are desperate to get the public behind them. Yet no matter how many auditions they hold, it’s no substitute for hard evidence.