President Trump’s current position on special counsel Robert S. Mueller III’s report is as follows:

1) it proved beyond all doubt that Trump is completely innocent;

2) it was illegal, biased and full of lies;

3) we should move on and get back to the work of governing; and

4) we must keep talking about it.

And in keeping the focus on the Mueller report, Trump has homed in on one particular threat: former White House counsel Donald McGahn testifying in public.

McGahn's story highlights what will be a key question for Trump and those around him as we dig down into this scandal, and perhaps others as well: How far will people around Trump go to defend him? Will they lie to the public? Will they lie under oath? Trump himself can't be sure, which is a key reason that he is now moving to shut down any possibility that those who work for him will have to testify before Congress.

Let's begin with what Trump tweeted Thursday morning:

To be clear, the president of the United States is implicitly accusing his former counsel — who testified to all the things that Trump is denying — of committing perjury. Which is a bit ironic, since it’s precisely the fact that McGahn was apparently not willing to commit perjury that turned him into Trump’s enemy.

This all has to do with a particular portion of the Mueller report, which details how Trump instructed McGahn to arrange for Mueller to be fired. (Despite what Trump says in his tweets, he couldn’t have fired Mueller himself; he would have had to order Deputy Attorney General Rod J. Rosenstein, who was overseeing the special counsel’s investigation, to do it.) Here’s what happened when a news report was published describing how Trump had ordered McGahn to arrange for Mueller to be fired, according to the Mueller report:

After the story broke, the President, through his personal counsel and two aides, sought to have McGahn deny that he had been directed to remove the Special Counsel. Each time he was approached, McGahn responded that he would not refute the press accounts because they were accurate in reporting on the President’s effort to have the Special Counsel removed. The President later personally met with McGahn in the Oval Office with only the Chief of Staff present and tried to get McGahn to say that the President never ordered him to fire the Special Counsel. McGahn refused and insisted his memory of the President’s direction to remove the Special Counsel was accurate.

We should note that McGahn is not some kind of hero. A loyal Republican, he went to work for Trump knowing exactly who his boss was. The fact that he resisted these instructions from Trump is the bare minimum of integrity that we would expect from anyone in public service.

So what we have here is Trump’s former counsel telling one story under oath to prosecutors, and Trump telling a different story. We should note here that Trump himself refused to answer questions in person from those prosecutors, because as his lawyers said many times, doing so would be a “perjury trap.” In other words, he would have inevitably lied under oath and then been vulnerable to a perjury charge.

Assumedly, if McGahn were to testify before Congress, he’d tell the same story he told Mueller’s team. Which is why the White House is planning to contest the subpoena McGahn has been issued by the House Judiciary Committee. And that’s also why the White House ordered a former personnel official, Carl Kline, to refuse a subpoena to testify about the way professional staff’s recommendations to deny security clearances to White House figures (including Jared Kushner) were overruled.

It’s also the same reason the White House is planning to refuse any and all subpoenas for documents or testimony from Congress (as Trump said, “We’re fighting all the subpoenas”). If they had to answer questions under oath, Trump’s aides might tell the truth.

Trump seems to have figured out that even the most loyal of his aides might be reluctant to perjure themselves on his behalf. Consider Sarah Sanders, who will dutifully go on TV and repeat any ridiculous lie Trump tells her to. When she was questioned by prosecutors about her preposterous assertion that “countless members of the FBI” had expressed support for Trump’s firing of FBI Director James B. Comey, she admitted this was false.

What's so revealing about this is that once she was under oath, Sanders fessed up. She's willing to lie to the public when Trump tells her to, but not willing to commit perjury.

Another important event that may be weighing on Trump’s mind: You’ll recall that Michael Cohen did perjure himself in congressional testimony to support Trump’s story about when the effort to get a deal for a Trump Tower in Moscow came to an end — but once he was nabbed, he admitted that he had lied and pleaded guilty.

McGahn has already shown that whatever else he did for Trump, he won’t commit perjury to help him. And Trump is probably concerned that there may be no one whose loyalty to him extends that far. Worst of all, congressional testimony would involve Trump aides potentially contradicting him in public, before the cameras. That’s much more dangerous than an anonymous quote in a news article.

That’s the real reason Trump will refuse to allow anyone to testify. Not because congressional investigations are too partisan, not because of executive privilege, but because he doesn’t want to test his aides’ loyalty. Trump may have surrounded himself with liars and hacks, but there’s only so far even they are willing to go.

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