We finally got a taste Sunday night of what former national security adviser John Bolton might tell President Trump’s Senate impeachment trial — if he’s called to testify, that is.

What we learned reinforced the potential peril for Republicans if they refuse to let him do so.

The New York Times reported Sunday that Bolton makes a series of very big Ukraine-related claims in an unpublished manuscript of his upcoming book, slated to be released in March.

Chief among them:

  • Bolton writes that he heard Trump say explicitly that the withholding of military aid would continue until Ukraine announced an investigation involving the Bidens — implicating Trump directly in a quid pro quo for the first time and contradicting the Trump team’s defense.
  • He writes that Secretary of State Mike Pompeo said privately that there was nothing to the Trump team’s claims that then-Ambassador to Ukraine Marie Yovanovitch was corrupt — suggesting that this was indeed a smear campaign and that Pompeo recognized it as such, even as he didn’t defend Yovanovitch publicly.
  • He writes that he raised concerns about Rudolph W. Giuliani’s efforts in Ukraine with Attorney General William P. Barr after Trump’s July call with Ukraine’s president — despite the Justice Department saying Barr learned about the call in mid-August.
  • He writes that acting White House chief of staff Mick Mulvaney was present for one of Trump’s calls with Giuliani about Yovanovitch, even though Mulvaney has told associates that he stayed out of those conversations to protect Trump and Giuliani’s attorney-client privilege.

In other words: Bolton is naming names — lots of names — and directly contradicting what top administration officials are saying.

And Trump has made no secret that he’s not particularly happy about the new revelations. After treating Bolton gently in the months since his White House exit, Trump lashed out. On Sunday night, he disputed Bolton’s account.

“I NEVER told John Bolton that the aid to Ukraine was tied to investigations into Democrats, including the Bidens,” Trump said.

Trump then proceeded to retweet other allies who derided Bolton, including Lou Dobbs, calling him a “rejected Neocon.” Trump also added as an addendum on Monday morning, after weeks of suggesting he’d like to see Bolton testify, that the Senate shouldn’t let him because it was the House’s job.

(Trump falsely claims the House didn’t ask Bolton to testify; it did, but when he refused, it declined to subpoena him.)

But while that’s clearly Trump’s calculation, the GOP senators who might vote on Bolton testifying in the Senate trial have their own to make. And the new Bolton disclosures severely complicate it.

In recent days, it has appeared less likely that Democrats would get the four GOP votes they needed to force Bolton’s testimony, which he has said he’s prepared to give. The new evidence, though, reinforces just how much insight he could provide — as well as the pitfalls of not allowing him to tell his story now.

The nightmare scenario for the GOP is that they give Trump the quick and witness-free acquittal that he apparently desires, but then information like Bolton’s keeps coming out. Bolton now suggests Trump was indeed telling people privately that the withheld military aid was part of a quid pro quo — a quid pro quo that Ambassador to the European Union Gordon Sondland testified that he communicated to the Ukrainians. This is something Trump’s team has strenuously denied, including at the impeachment trial. What if Bolton isn’t the only person Trump told this to who might suddenly contradict them? However closely this has already been tied to Trump, it can always be tied more closely. Bolton’s upcoming book — slated for March 17 — is a great example of how the hastily assembled walls the Trump team have built around its defense can quickly crumble and, in some cases, already have.

The evidence, after all, is pretty compelling that Trump wasn’t truly concerned about corruption in Ukraine. Giuliani actually said publicly that these investigations weren’t about foreign policy but were instead about helping “my client.” There are also several confirmations that these were quid pro quos — including both military aid and a White House meeting — and that the quid pro quos were communicated to the Ukrainians, even if previous witnesses couldn’t say whether Trump explicitly signed off on them. Indeed, both Bolton and Mulvaney — two very high-ranking White House aides — have now offered confirmation of the quid pro quos, even though Mulvaney recanted his.

The danger in this for the GOP is that this all keeps coming out, as it has been, in a steady stream of drips as we get closer and closer to the 2020 election. In just the past couple of weeks, we’ve seen indicted Ukrainian American business executive Lev Parnas supplying high-profile claims about all this — with documentation and audio to back some of the big ones up — and now we’ve got Bolton finally stepping forward and connecting this to Trump.

Imagine if Republicans vote against entertaining Parnas’s evidence or putting Bolton on the stand, and then the information comes out anyway. If it proves damning, it will look like they engaged in the coverup that Rep. Jerrold Nadler (D-N.Y.) accused them of last week.

And at the least, if Trump is saying Bolton is lying, what better way to hold him accountable than to make him say all of this under oath? He’s indicated he’s willing. Now it’s in the Senate GOP’s hands, and you can bet it’s a tougher call now.