Throughout special counsel Robert S. Mueller III’s investigation into the Russia scandal, President Trump and his defenders have cast about for evidence they can use to dismiss the entire probe as tainted. Did a person on Mueller’s staff once contribute to a Democratic candidate? Did an FBI agent privately express a negative opinion about Trump? Was there a single source with less than pure motives? If so, then the entire thing can be dismissed as a witch hunt, a frame job, a conspiracy to destroy the president.

Here’s the latest iteration of this: Trump and his allies are talking up an informant who was somehow connected to the Trump campaign in 2016 and provided information to the FBI both before and after the Mueller investigation began. The president himself is making some wild accusations about this informant.

So here’s what we know and don’t know about him or her, and how it fits into the broader investigation.

This isn’t just any informant. The Post reports today that Justice Department officials believe exposing the informant could compromise other investigations and even risk lives. We can’t know to what degree that’s true. But the idea that they want to keep this person’s name secret because they’re out to get the president is ludicrous. That’s especially true given that Trump himself was persuaded that the source’s identity should be kept secret, as The Post reported last week: “Intelligence officials fear that providing even a redacted version of the information [House Intelligence Committee Chairman Devin] Nunes seeks could expose that person and damage relationships with other countries that serve as U.S. intelligence partners.”

By now Trump may have changed his mind about that. But here’s a passage from today’s Post article:

The source is a U.S. citizen who has provided information over the years to both the FBI and the CIA … and aided the Russia investigation both before and after Mueller’s appointment in May 2017, according to people familiar with his activities.

This means that this isn’t, say, someone who worked in the mailroom and overheard something shocking, then decided to tell the FBI. It also means that while it isn’t a foreign national, it’s someone who has some kind of overseas ties, since he or she provided information to the CIA in the past. How valuable is this source? Here’s a hint:

The stakes are so high that the FBI has been working over the past two weeks to mitigate the potential damage if the source’s identity is revealed, according to several people familiar with the matter. The bureau is taking steps to protect other live investigations that the person has worked on and is trying to lessen any danger to associates if the informant’s identity becomes known.

That also means this isn’t someone we’ve already heard of.

We don’t know what the informant’s relationship to the Trump campaign was. Was he or she on the staff? An outside adviser? Just someone who came in contact with people on the campaign for some other reason? We have no idea. Trump and some of his defenders are insisting that the FBI planted the source in his campaign to gather information on him, which would suggest an employee:

But we have no idea whether the informant was “implanted.” This morning, Trump’s lawyer Rudy Giuliani said, “We’re told there were two infiltrations, two embedded people in the campaign.” Pressed on where he learned this, Giuliani was vague. Given how often he has said things that he quickly walked back or turned out to be bogus, there’s no reason to think he has any idea what he’s talking about. But it’s theoretically possible.

We know essentially nothing about what information the informant provided. We don’t know what the informant has passed on to investigators. We don’t know how central this information became to the investigation, or if it revealed any crimes. The information could be the key to the whole case, or it could be of little or no importance.

Nunes wants to expose this informant. Nunes has made it his mission to destroy the Mueller investigation and perhaps the entire Justice Department if that’s what it takes to defend Trump. He is now demanding that the Justice Department hand him information on this informant, which it has refused to do. Nunes has even threatened to hold both Attorney General Jeff Sessions and Deputy Attorney General Rod Rosenstein — both Trump appointees — in contempt if he doesn’t get the informant’s identity.

The underlying premise of all of this is absurd to begin with. Republicans are trying to argue that the fact that the FBI was investigating the Trump campaign during 2016 is evidence that it was out to get him. But that could only be true if you start from the presumption that everything the FBI does is out of bad faith, and that even way back then the bureau was trying to destroy Trump.

But if you don’t assume the FBI was acting in bad faith, then you have to conclude that whatever it learned in 2016 was so disturbing that it decided to open an investigation into a presidential campaign’s ties to a hostile foreign government, an extraordinary step to take. In striking contrast to the way then-director James Comey treated Hillary Clinton, they were incredibly scrupulous about making sure that news of their investigation was not revealed publicly so as not to damage Trump’s campaign.

We don’t know how the showdown over this informant is going to end. But one way or another, whether his or her identity is revealed or not, we’re going to learn what that person learned about the Trump campaign. And if Trump and his defenders thought there was nothing damaging to be revealed, they wouldn’t be trying so hard to preemptively discredit this informant, in the same way they’re doing to the whole investigation.

In other words, just as they have been all along, they’re acting as though Trump and others around him are guilty as sin. I wonder why?

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