If coup-coup Nancy Pelosi has a panic button, now would be a good time to lean on it. With signs that Americans are tuning out the impeachment hearings, the clock is ticking on Democrats’ chance to make their case.

Pelosi is clearly worried, telling fellow Dems it’s a “weak response” to “let the election decide” whether President Trump should be removed.

“That dangerous position only adds to the urgency of our action, because ­POTUS is jeopardizing the integrity of the 2020 elections,” the speaker wrote in a “Dear Colleague” letter to her House members.

The letter seemed strange enough when it became public Monday, but Tuesday’s hearing more than justified her fear and desperation. With her party now having failed to hit anything close to pay dirt after three long days of public testimony, she is trying to keep her members on board the impeachment train, lest the whole effort crash in failure and disgrace.

Alas, Tuesday wasn’t much help. As they did in the first hearings last week, Dems again failed to make the Ukraine ­issue the crime of the century or even of the Trump presidency. Their hyperbolic descriptions are not even close to the pedestrian evidence they’re producing.

Their problem last week largely centered on the fact that none of the witnesses were actual witnesses to any relevant events, including the July 25 phone call between Trump and Ukraine President Volodymyr Zelensky.

They solved that problem early Tuesday with the day’s first two witnesses, Jennifer Williams and Lt. Col. Alexander Vindman, both of whom listened to the call in the White House. Finally, the impeachment zealots had someone with firsthand knowledge, as opposed to the second- and third-handers last week.

They got even closer in the afternoon, with former officials Tim Morrison and Kurt Volker higher up the food chain. In contrast to all the other witnesses, both had actually met Trump!

But still the end zone proved elusive. The closest Dems came was when Williams, an aide to Vice President Mike Pence, said she found the July 25 call “unusual.” Vindman declared it an “inappropriate and improper” demand and reported it to lawyers.

Quickly, though, Republicans cleverly succeeded in contrasting those two reactions, with Texas Rep. John Ratcliffe saying, “There is no consensus about what you heard,” and that any impeachment case “must be clear, overwhelming and compelling.”

Earlier, Ratcliffe had stacked the transcripts of 10 long depositions and noted that not a single witness had accused Trump of “bribery,” the focus-group-tested word Dems have now adopted as their battle cry.

The cumulative effect was to create a sense of doubt about the heart of impeachment. Was there really a crime, or was it just a difference of opinion? And how much of it is purely partisan?

The doubts took a leap when Vindman conceded that lawyers said it was legal for Trump to temporarily withhold more than $400 million in aid to Ukraine.

Once fair-minded Americans seriously entertain the question of whether the actions involved even amount to a crime, most will probably find it difficult to conclude Trump represents an urgent threat and must be removed immediately. All the more so when they can read the call transcript for themselves, as well as learn that Ukraine got the promised aid and never launched any of the investigations Trump requested.

And so Day Three of the public hearings went pretty much as the first two. Long hours of testimony, some it interesting and relevant, punctuated by mutual expressions of contempt between Democratic Chairman Adam Schiff and Republican members.

Vindman was a strong witness, but a strange one, too. He presented himself as an Alexander Haig-like “I’m in charge here” figure, when he was actually far down the pecking order.

His inflated sense of self-importance seemed to be key to his alarm over the phone call. As he put it, he believed “that if Ukraine pursued an investigation in the 2016 elections, the Bidens and Burisma, it would be interpreted as a partisan play” and Ukraine would lose bipartisan support, which in turn would “undermine US national security and advance Russia’s strategic objectives.”

He conceded, smugly, that he even advised Zelensky “to stay out of US domestic politics.”

He said Trump would be acting against US policy if he got the investigations. Although he later conceded that Trump as president could change the policy, he didn’t seem to mean it.

And yet Vindman, wearing his Army uniform and medals, including a Purple Heart he was awarded after being injured in Iraq, was the Dems’ star of the day.

He could be a major figure in the secretive run-up to the hearings, a notion bolstered when Vindman, with Schiff running interference, refused to name a person in the intelligence community he told about the call.

Because the so-called whistleblower was a CIA officer, some in the GOP believe Vindman set the whole saga in motion and helped to shape the Dems’ case.

Adding to the surreal quality of the hearings is a crucial fact that gets too little attention: Trump’s policy toward Ukraine has been far stronger than President Barack Obama’s. Providing Ukraine with antitank weapons to counter Russian invasions is a direct slap at Vladimir Putin, a move Obama rejected because he feared it would provoke Putin.

Thus, removing Trump would benefit Russia, proving that, for Dems, Ukraine’s security is just another pawn in their war against the president.