David Margolis was my mentor, and my occasional companion at Nationals games, where we shared season tickets since 2005. He served in the Department of Justice for more than 50 years, and when he passed in 2016, the department lost — as The New York Times so aptly put it — a “revered prosecutor” and an “all knowing, Yoda-like figure.”

I lost a dear friend. I find it useful to recall lessons David shared with me. He was brilliant and wise — different traits — and one of his favorite sayings resonates with me now: “Facts are stubborn things.”

As events surrounding the impeachment inquiry unfold quickly — and occasionally too quickly to digest fully — there is a tendency to assume things we do not yet know and to color things we think we know.

As events surrounding the impeachment inquiry unfold quickly — and occasionally too quickly to digest fully — there is a tendency to assume things we do not yet know and to color things we think we know. Both tendencies can be perilous. Not everything that is kept secret is sinister, and many different presidents — Democrats and Republicans — have withheld information for legitimate reasons dating back to George Washington. Sometimes, however, the rationale for withholding information seems more suspect and raises compelling questions about transparency. Here’s a more recent example.

On Monday, four witnesses were scheduled to testify in closed-door depositions before the House Intelligence Committee. It now seems that none of those four are going to show up, a move which has intensified claims from Democrats that the White House is trying to cover up the truth relating to President Donald Trump’s now-infamous phone call with the Ukrainian president.

One of those four is a deputy White House counsel named John Eisenberg who currently serves as the legal adviser to the National Security Council. John and I overlapped briefly at the Justice Department and I know him slightly — enough to have a favorable opinion of him, for what it is worth.

When Lt. Col. Alexander Vindman — a member of the National Security Council staff who overheard a troubling phone call between Trump and the president of Ukraine — properly reported his concerns to Eisenberg, Eisenberg reportedly told Vindman not to discuss that phone call with anyone else. By all accounts, Vindman is wholly credible and, in my view, manifestly fulfilling his duty to report perceived misconduct to Eisenberg. Good reporting in Politico, and in other places, has described this conversation between Eisenberg and Vindman.

Now, I think there are at least two plausible explanations for Eisenberg’s advice to Vindman to remain silent. One plausible explanation — and it seems to be where some of the commentary has drifted — is nefarious. By telling Vindman not to speak further about a troubling conversation that he overheard, Eisenberg could be attempting to cover up the president’s misconduct.

By the way, I do believe, based on the publicly available reconstruction of that call, that the president’s conversation with his Ukrainian counterpart is deeply troubling. It seems to be an abuse of power for the president to try to leverage the provision of appropriated military aid to Ukraine in return for political dirt on Joe Biden — a potential 2020 democratic nominee for president. That’s not a good thing.

But there is a second explanation for Eisenberg’s advice to Vindman that is also plausible, and that also makes sense to me — and that is not nefarious. When a good lawyer learns of potential misconduct (and Eisenberg is, by all accounts, a good lawyer), that lawyer has an obligation to gather the facts and recommend a course of action to his boss (here, the White House counsel) and to his client (here, the Office of the President). Eisenberg, unlike Rudy Giuliani, does not serve Trump personally in his capacity as counsel — an important distinction.

There is a second explanation for Eisenberg’s advice to Vindman that is also plausible, and that also makes sense to me — and that is not nefarious.

According to Politico, Eisenberg is indeed cautious. Someone in his position should be. But you do not have to be overly cautious to be concerned about leaks or witness contamination. I have worked on numerous investigations — as a federal prosecutor — where I have asked witnesses not to share the story that they told me with other witnesses; indeed, not to share their story with anyone else while I am working to gather facts. Why would I ask this? Because, when I speak to each witness, I want his or her unvarnished recollection of what happened, free from the recollection of any other witness.

If I speak with witness A, and they then discuss my questions and their answers with potential witness B, there is a chance that when I speak with witness B, witness B will provide to me information that has been influenced by conversations with witness A. This can be wholly innocent behavior — the two witnesses may genuinely be trying to recall what happened so that they can faithfully share it with me — but there is still a danger that the first witness inadvertently colors the memory of the second witness. Good prosecutors and agents know this and work assiduously to avoid that sort of taint.

Is it possible that Eisenberg was asking Vindman not to speak with other witnesses for this benign reason? Certainly. Do we know that to be the case? Not yet. Could it have been nefarious? Perhaps. But it would be wise for Congress to interview more witnesses, to ask thoughtful questions to determine motive and intent, and to follow the facts wherever those facts lead.

Nobody benefits from a rush to judgment. Investigations are hard and good investigations are even harder. As David Margolis would say, “Facts are stubborn things.” Let’s gather them, before we decide what — and why it — happened.