And yet troubling leads keep turning up anyway.

Parnas’s recent media interviews did two crucial things that deserve urgent attention. First, he directly linked President Trump to the delivery of an ultimatum to Sergey Shaffer, a senior aide to Ukrainian President Volodymyr Zelensky. Parnas told MSNBC’s Rachel Maddow that he was instructed to deliver what he described as “a very harsh message,” and to do so in “a very harsh way, not in a pleasant way.” Parnas explained, “Mayor Giuliani, Rudy, told me after, you know, meeting the president at the White House. He called me. The message was, it wasn’t just military aid, it was all aid. Basically, their relationships would be sour, that he would—that he would stop giving them any kind of aid … unless there was an announcement made.”

The key words here? That Giuliani spoke to Parnas “after meeting with the president at the White House.”

David A. Graham: We can’t afford to ignore Lev Parnas’s explosive claims

All along, Republicans have struggled to come up with a sound explanation that would justify Trump’s withholding of $391 million in Senate-approved aid to Ukraine until Zelensky did him the “favor” of investigating the Bidens. They’ve also emphasized a perceived lack of evidence directly linking Trump to the quid pro quo. But the notion that Trump was genuinely interested in fighting corruption in Ukraine looks more and more preposterous, as does Republicans’ winking suggestion that he had no idea what was happening. On Thursday, the nonpartisan Government Accountability Office released a report stating that Trump’s halting of aid to Ukraine broke federal law for no good reason. “Faithful execution of the law,” the report said, “does not permit the President to substitute his own policy priorities for those that Congress has enacted into law.”

The other major thing Parnas has done is implicate figures beyond Trump and Giuliani in the Ukraine scandal—specifically in efforts to destroy the career of Marie Yovanovitch, the U.S. ambassador who Trump infamously said would “go through some things” in his July 25 call with Zelensky, and to trash the reputations of a primary rival for the presidency, Biden, and his only remaining son, Hunter. Parnas has been emphatic that Vice President Mike Pence was “in the loop” on all of it, that Attorney General William Barr “had to have known everything,” and that Representative Devin Nunes “knew very well” what was going on. And like Ambassador Gordon Sondland in his testimony in the House impeachment inquiry, Parnas corroborated that the president’s goal was to strong-arm Zelensky into announcing an investigation into Biden—not to root out Ukrainian corruption, as the president and his defenders weakly claim.

Parnas, who started a company called Fraud Guarantee, is not the most reputable of potential witnesses. Predictably, Trump’s allies have responded by calling Parnas a liar and highlighting the criminal charges against him, which include conspiracy to violate laws banning foreign donations to federal and state elections on behalf of Republicans. The wrinkle for Trumpians is that documents don’t lie, and they don’t misremember. Parnas gave Congress a trove of notes and communications that could corroborate some of his testimony. Moreover, the existing House impeachment record includes phone logs of Parnas’s communications with Nunes as well as the July 25 call summary memorializing Trump’s suggestion that Zelensky call Barr.