Much of the focus in the lead-up to the president’s impeachment trial in the Senate next week has been on securing the testimony of former national security adviser John Bolton and other Trump confidants. But Democrats need to keep in their sights a source of evidence that’s just as important, and maybe more important, than witnesses.

Documents.

House investigators’ release of documents Tuesday from Lev Parnas, a business associate of Trump personal lawyer Rudolph W. Giuliani, brings home again the singular force of the written record. The cache is incendiary, and the newly named House impeachment managers will be able to do much more with it than they would with testimony of the easily discredited Parnas, who is facing campaign finance charges in federal court. (He has pleaded not guilty.)

When Giuliani writes in a letter to then-President-elect Volodymyr Zelensky that he is acting in his “capacity as personal counsel to President Trump and with his knowledge and consent,” it is a double whammy for Trump: It both forcefully refutes the argument that Trump was pursuing an anti-corruption program in the nation’s interest, as opposed to his personal interests, and it establishes (unless Giuliani was lying in the letter) that Trump knew of Giuliani’s campaign.

Similarly, the sheet of Ritz-Carlton stationery on which Parnas jots “get Zalenksy [sic] to Annouce [sic] that the Biden case will be Investigated” puts the lie to the narrative that Trump and Giuliani were pursuing general anti-corruption efforts rather than seeking to smear the president’s political rival.

Put just these two together, and they sharply undermine pretty much the only defenses on the merits that any Republican senator has even tried to make.

As any prosecutor will tell you, it’s documents that make a case. That’s true in two senses: First, it’s the collection and analysis of the documentary evidence that determines whether to charge and how to put a white-collar case together in nearly every instance. Second, documents nearly invariably serve as the scaffolding of the case at trial.

Not to say that it’s a good idea to base a prosecution on documents alone. Any good trial lawyer seeks to make the written word come alive, especially with credible testimony. But experienced trial lawyers go into battle whenever possible with a binder of “hot documents,” which they put before the jury again and again and bring home in closing arguments. That’s the core of their case.

The recently released email correspondence between the Office of Management and Budget and the Defense Department is a good illustration of the force of the documentary trail. The emails supply a step-by-step account of an effort by political officials at OMB to run roughshod over legal requirements involving Ukraine funding. And they climax with the email explaining that the continued hold on the funds was at the “clear direction from POTUS.”

Here, too, with regard to Bolton or any particular witness, memorandums of conversations (e.g., any reference to the “drug deal,” as Bolton reportedly described the Giuliani escapades), memos detailing conversations (as former FBI director James B. Comey made after talking with Trump) and, especially, all email traffic with Bolton (generally the most fertile source of evidence because of the kind of unguarded statements it tends to reveal) will almost certainly sketch out his actual conduct and knowledge.

Documents, unlike witnesses, don’t go south on you. The much-anticipated Bolton testimony is a prime example. If and when Bolton raises his right hand, he already will have crafted what he wants to say down to the word. And if, as is likely, he doesn’t want to mortally wound the president, he will do his best to avoid doing so.

And as Bolton illustrates, witnesses can also have multiple objectives — Bolton will be sworn to tell the truth, yes, but will he also have one eye on book sales, or his status with the public and his party, or some resentment with onetime rivals in Trump’s orbit? They also have personality quirks that inevitably color testimony. Bolton, for instance, has a reputation as something of a hothead. That personality type presents certain opportunities for the deft trial lawyer, but it also can post an obstacle to getting at the truth.

Finally, remember, witnesses can be rehabilitated by the other side. If a witness at first seems to bolster the House’s case, we can expect the softest of softballs from the Republican side to create at least some ambiguity. That’s tougher to do when the evidence is right there in black and white.

The documents are the mother lode here — both for setting up effective testimony of any witnesses and for the nuggets of truth that they will contain. The Democratic House managers need to insist on complete compliance with their document requests.

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