If you think the impeachment proceedings against President Trump haven’t changed any Republicans’ minds, look again. In the past week alone, influential evangelicals and conservative pundits have called for Trump’s removal. Only one notable group of Republicans is — at least for now — still united in indulging Trump: those serving in Congress.

But it’s the 53 sitting Republican senators who are poised to determine the president’s fate, as 20 of their votes will be needed to remove Trump from office. That makes it essential that they see in the Senate chamber a real impeachment trial, with real witnesses and other real evidence — something that four Republican senators can make happen by siding with Democrats and with the overwhelming public support for having witnesses testify. And there’s plenty of new material for senators to consider in a trial.

Start with the bombshell that exploded late Friday night.

An email the government had tried to hide but was forced to hand over in a lawsuit shows precisely why testimony from a crucial witness like the Office of Management and Budget’s Michael Duffey can still add critical details to our collective understanding of Trump’s Ukraine misdeeds. Duffey’s email reveals stunning illegality at the direct behest of the White House. It’s no surprise that he’s one of the four witnesses Senate Democrats have asked to testify, even before the email was released. The email underscores just how essential it is to have Trump’s impeachment trial work like any other trial does: with the presentation of evidence.

The email in question was sent 91 minutes after Trump’s infamous July 25 phone call with Ukrainian President Volodymyr Zelensky. On that call, Trump asked Zelensky to “do us a favor” by opening investigations into alleged 2016 election interference by Ukraine — a baseless Trump theory — and political rival Joe Biden, in exchange for providing the weapons that Congress had ordered sent to Ukraine to defend against Russian aggression. The email shows that Duffey, on behalf of the White House, ordered the Pentagon to suspend all the military assistance Congress had allocated.

The timing adds to the considerable body of evidence showing the direct quid pro quo that Trump pushed for, and strongly supports the first of the two articles of impeachment approved by the House. The message reveals that Trump was abusing the power of his office by attempting to withhold congressionally allocated weapons, and the obvious reason he did so was for his personal political gain. But the email goes even further: By directly ordering the Defense Department not to notify Congress about the hold on weapons for Ukraine, the Trump White House was breaking the law.

The precise wording of Duffey’s email is crucial. He wrote to the Pentagon comptroller: “Given the sensitive nature of the request, I appreciate your keeping that information closely held to those who need to know to execute the direction.” Both of us have worked in national security positions, and we know what that bureaucratic language means: “Those who need to know to execute the direction” were Pentagon officials. After all, they were the ones who needed to know not to deliver the weapons. So whom did Duffey not want told?

We think his email is most fairly read as a reference to Congress, and perhaps some others in the executive branch. Basically, a White House official was telling the Pentagon comptroller: Don’t tell Congress about all this.

If there’s any doubt about what the email meant, Duffey could clear it up by testifying. But he has dodged all attempts to do so. And the email reveals even more problems for the White House. The law governing impoundment — the executive branch’s decision not to spend congressionally appropriated funds — requires the executive branch to notify Congress of any decision to withhold expenditures of funds appropriated by Congress. The law states that, whenever the executive branch “proposes to defer any budget authority provided for a specific purpose or project, the President shall transmit to the House of Representatives and the Senate a special message specifying” details, including the amount of funding held back, the period intended for holding it back and the reasons, including any legal authority justifying the delay. The law also requires an analogous message containing similar details whenever the executive branch proposes not merely to delay an expenditure but to rescind it entirely. As one scholar summarized these two provisions of law, “The executive must transmit a special message to Congress whenever it proposes to rescind or defer funding.”

The Trump White House sent no such message to Congress — not on July 25, not thereafter. And Duffey’s email made sure that the Defense Department would send no such message, either. Duffey surely knew what the law required — after all, he’s a high-ranking official at the Office of Management and Budget. And Duffey surely knew that the Pentagon comptroller knew what the law required — this sort of stuff is a comptroller’s daily fare. So it wasn’t enough for Duffey to order Defense Department officials to withhold the weapons from Ukraine. He needed to order them to withhold the legally required alert to Congress. And that’s just what he did.

(Duffey did not respond to a request for comment for a Washington Post report about the email over the weekend. White House officials told the New York Times that the timing of the call with Zelensky and of Duffey’s email was a coincidence.)

What the email didn’t do was provide any justification for hiding the hold from Congress. This, too, is crucial: It raises questions about the memo issued this month by the Office of Management and Budget’s general counsel attempting to justify withholding assistance to Ukraine and notification to Congress. That memo claimed no congressional notification was necessary because the hold was a “programmatic” one, meaning it was consistent with congressional intent in allocating aid to Ukraine. The memo already has been blasted as a shabby attempt at after-the-fact rationalization. The absence of any corresponding justification in Duffey’s email makes it look even more so.

So who told Duffey to send the email? How fully did they explain the link between the email he was to send and the call between Trump and Zelensky that had concluded 91 minutes earlier, as well as the link to Duffey’s own earlier email to the Pentagon — also revealed Friday — conveying that Trump himself had asked about the Ukraine military aid? What else did they say to Duffey? And what did Duffey tell others at the Office of Management and Budget? Remember, according to testimony before the House, an OMB lawyer quit at least in part over this.

Americans need to know. And senators need to know before they cast a vote that will determine Trump’s fate and their own historical legacies. Minds are changing — even Republican minds. Senators need witnesses who will be able to tell the truth. We inched closer to that on Friday, with Duffey’s email finally seeing the light of day. Now we need the rest — with Duffey and other witnesses testifying in a real impeachment trial, in the Senate chamber, for all to see.

In the House, Trump tried to gag every executive branch employee from testifying, no doubt because he was afraid of what they would say. The Senate should not put up with Trump’s ever-escalating coverup. Let the witnesses testify, and let the chips fall where they may.

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