Sitting just out of President Trump’s grasp is something that has eluded him for much of his tenure in politics: certainty.

He won the presidency — despite his popular vote loss. He escaped the Russia investigation — but wasn’t exonerated by special counsel Robert S. Mueller III, despite his tweets making that claim. Now he’s been impeached but, for once, can look forward to a robust determination that unequivocally goes his way. Barring something truly earth-shattering, Trump will be cleared by the Senate of the charges filed by the House. Sure, it will be largely because of the unity of the Republican caucus, but he can argue that the impeachment itself was a function of partisan unity. At last, vindication — or, at least, the closest he’s gotten.

But we’re not quite there yet. A significant though not insurmountable obstacle appeared out of the blue on Sunday. According to the New York Times, an upcoming book by former national security adviser John Bolton will describe how Trump did precisely what House Democrats allege: withholding aid to Ukraine until he got assistance with investigations that would benefit him politically.

Trump’s defense team in the ongoing Senate impeachment trial largely ignored the Bolton revelation, although his lead attorney, Jay Sekulow, did address it on Tuesday. He noted that after the Times article was published, Vice President Pence released a statement indicating a lack of awareness about any such quid pro quo.

“That was the response, responding to an unpublished manuscript that maybe some reports have an idea of maybe what it says,” Sekulow said. “That’s what the evidence — if you want to call that evidence. I don’t know what you call that. I call it inadmissible, but that’s what it is.”

That’s hardly going to be sufficient for many senators and most Americans. Trump and Senate Majority Leader Mitch McConnell (R-Ky.) have been scrambling to figure out how to keep enough Republicans from supporting a subpoena for Bolton that he might end up testifying. Late Tuesday afternoon, reports indicated that McConnell did not yet have the votes.

What's remarkable about this, of course, is that having Bolton testify would be the best way for Trump and his allies to address his claims. Unless, of course, Bolton's allegations are true.

Remember: While Trump wants to wrap this thing up as quickly as possible, it’s not the case that Bolton’s claims will remain under wraps if he isn’t called to testify. He wrote them in a book, due for release in mid-March. Even if Bolton doesn’t testify, the claims he makes impugning Trump will be made public — unless the White House tries to block them on national security grounds. That certainly seems like it’s within the realm of possibility, but, given that this claim is already public, it seems as though that might not survive a court challenge.

On Wednesday morning, Trump attacked Bolton and his allegations on Twitter. Bolton was given the post of national security adviser over objections, Trump claimed, and proceeded to do a bad job. After leaving the White House, Trump wrote, Bolton “goes out and IMMEDIATELY writes a nasty & untrue book. All Classified National Security. Who would do this?”

That “classified” claim seems like a nod in the direction of blocking release of the book. (Update: The White House on Wednesday did just this.) It’s admittedly hard, though, to figure out how the book could both be classified and false.

That claim that Bolton is lying is, in fact, a very good reason for Bolton to be called to testify. After all, what the Senate trial offers is the opportunity for Trump’s team to interrogate Bolton under oath. When the book comes out, Bolton will no doubt tour talk shows, elevating his allegations against Trump. If those allegations are false, he will be able to lie about Trump without repercussions. Asked about the claims during the Senate trial? He could face criminal charges if he is shown to be lying. Isn’t that a better way to force Bolton to acknowledge what really happened?

There are two overlapping reasons that having Bolton testify might nonetheless not be appealing to Trump and his team. The first is that they may prefer to attack Bolton publicly once the book comes out without being fettered by the responses to past questions that he answered under oath. The other is that Bolton may be telling the truth — and so they want to attack him without his being able to point to having testified under oath.

To be clear, there’s no good reason to think that between Bolton and Trump, Bolton is the one who isn’t telling the truth. Trump is frequently dishonest, particularly when his back is against the wall. There’s plenty of evidence to suggest that Trump held the aid to Ukraine specifically for the purpose that Bolton alleges. Bolton, you may remember, was ousted from the administration on Sept. 10 — one day after House Democrats announced an investigation into the hold on aid and one day before the aid was released. Perhaps the timing of Bolton’s departure was a coincidence, and maybe it was a coincidence that O.J. Simpson’s glove was at his ex-wife’s house.

Trump's plan, then, seems to be to power through the trial without witnesses, get that clean bill of health from Senate Republicans and then fight both the release of Bolton's book and the aftermath. Bolton will become just another target of Trump's frequent and then occasional fury, another person shunted into the gallery of traitors to the cause.

The president won’t be the only one affected by this plan of action, as McConnell well knows. Once March rolls around, for those several weeks where Bolton is on television talk shows detailing what he says Trump did, there will be enormous scrutiny of those senators who decided against having Bolton come testify. Senators like Cory Gardner (R-Colo.) and Thom Tillis (R-N.C.) would see attack ads on heavy rotation arguing that they put defending Trump ahead of answering the questions raised by the impeachment.

Perhaps they’ll get an October Trump rally for their efforts. Or perhaps they’ll get nothing besides the satisfaction of knowing that Trump’s acquittal happened a week or two before it otherwise would have.