Sooner or later—probably after the House Intelligence Committee starts public hearings—Donald Trump is going to run out of defenses.

Trump and his defenders will no longer be able to deny that the Trump administration conditioned military aid and a White House meeting on the president of Ukraine agreeing to investigate Trump’s political rivals.

The proof already exists in abundance for anybody taking the care to read reports of the non-public depositions of non-partisan career diplomats and security officials.

Timothy Morrison, a senior NSC aide, has testified that Trump super-donor Gordon Sondland, who worked directly with Trump on Ukraine, told him that military assistance to Ukraine would not be released until the country committed to investigations of Trump’s political opponents.

Morrison’s testimony corroborated testimony previously given by William Taylor, the top American diplomat in Ukraine. All of this, in turn, corroborates the testimony of other highly credible witnesses, including former NSC aide Fiona Hill, and current NSC Ukraine expert Lt. Col. Alexander Vindman. There is likely more to come, possibly from former National Security Advisor John Bolton.

Despite this abundance of evidence, the facts haven’t yet found their way into the public consciousness sufficiently to scare congressional Republicans out of their denials. But that could change when the nation views a parade of credible witnesses give clear, corroborated, and highly damning testimony on television. Character assassination will become a less effective tool as the testimony piles up, one believable witness after another, much of it from conservative Republicans and decorated military veterans, many of whom were appointed to their positions by Trump himself.

It also seems likely that Trump defenders will have to abandon their denials that the administration attempted to cover up a corrupt quid pro quo by placing the summary of Trump’s conversation on a secret server.

Colonel Vindman’s testimony on this subject is incredibly damning. Vindman testified that minutes after listening in on Trump’s July 25 conversation with the president of Ukraine, he rushed to the office of White House lawyer John Eisenberg to alert him about the call. Vindman told Eisenberg that what the president had said on the call was wrong.

Eisenberg’s response was to attempt to bury it:

Scribbling notes on a yellow legal pad, Eisenberg proposed a step that other officials have said is at odds with long-standing White House protocol: moving a transcript of the call to a highly classified server and restricting access to it, according to two people familiar with Vindman’s account.”

The cumulative effect of all of this testimony—and remember, the inquiry has only just begun—is not only corroboration of nearly every important detail in the anonymous whistleblower report, but also the destruction of the argument that the report couldn’t be relied upon because it was mostly second-hand. We now have first-hand accounts.

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The president’s defenses were first predicated on denying the facts. Those defenses are no longer operable. The second defensive line was about process and the unfairness of having the initial inquiry behind closed doors. As the inquiry moves into public view, that line, too, will fall.

The third fortification is the admission that what Trump did is unfortunate, or possibly even wrong, but “not impeachable.” This will be a difficult line to hold, too. Because if selling out our national interest for private political gain isn’t impeachable, then what is? If extorting a foreign power into interfering with an American election isn’t impeachable, what is?

The “not impeachable” argument will be revealed to be as flimsy as—and ultimately dependent upon—the factual denials. When they go, it goes.

So what possible defense is left?

What’s left is to demand of the pro-impeachment forces that they provide incontrovertible, first-hand evidence laying the corrupt quid pro quo and the cover-up directly at the feet of Donald Trump. Because while his stink may be all over it, his fingerprints aren’t.

Except for the July 25 phone call, of course. But Trump’s supporters have found, manufactured or imagined enough ambiguity in that call to stay in their defensive posture. It hasn’t been enough to move them.

And there may never be enough. How many people, after all, do you think Trump ordered directly, face-to-face, to withhold military aid and a presidential visit until the president of Ukraine agreed to investigate Trump’s political enemies? In exactly those words?

Definitely Rudy Giuliani. Possibly Mick Mulvaney. Possibly Gordon Sondland. Maybe Mike Pompeo. Or Rick Perry. Or Bill Barr. Perhaps one of his patrilineal advisors.

Who on that list is likely to rat him out?

Not one of them.

Remember, the individuals that Trump was likely to have trusted to keep his secrets are not only his sycophants, they are also people who are vulnerable to political and criminal liability of their own. If they admit to having had a role in extortion and a cover-up, they get themselves in trouble. Dropping a dime on Trump is dropping a dime on themselves.

And even in the unlikely event that one of the Trump insiders did turn on him, Trump would destroy him: He’s a liar. Or maybe he thought that’s what I wanted, but it wasn’t. It. Wasn’t. Me.

Congressional Republicans wouldn’t believe Trump—but they’d pretend they did. And they’d have his back out of fear that he’d turn on them, too.

Which boils down to Trump’s ultimate defense: Everybody under the bus.

It would go something like this:

Gosh, I never knew all these people were doing terrible things in my name. Giuliani, Sondland, Taylor, Morrison, Vindman, Eisenberg, and Hill all did terrible things, or knew that others were doing terrible things. Nobody told me about it. Lock them up, but I had absolutely nothing to do with it. If I did anything wrong (which I didn’t), it was that I was too trusting.

Trump’s going to need a really huge bus to throw all those people under it, but don’t put it past him.

And don’t put it past his congressional defenders to try to help him do it.