Some of the most disturbing and clarifying information Parnas has provided since turning on Trump involves the administration’s fixation on Marie Yovanovitch, the former American ambassador to Ukraine. It’s true that people around Trump saw her as an obstacle to getting Ukraine’s government to open a politically motivated investigation into Joe Biden and his son, Hunter, but that doesn’t quite explain the scale of the animosity toward her.

Trump didn’t just fire her. He told Volodymyr Zelensky, the Ukrainian president, that she was going to “go through some things.” We learned this week that Robert Hyde, a deranged Trumpworld hanger-on and Republican congressional candidate, sent a series of messages to Parnas suggesting he was stalking Yovanovitch. (Ukraine has opened an investigation into Hyde’s activity, and on Thursday he was visited by the F.B.I.) A lawyer and Fox News regular named Victoria Toensing — who has represented a Kremlin-aligned Ukrainian oligarch who is, according to the Justice Department, an upper-echelon associate of Russian organized crime figures — texted Giuliani saying, “Is there absolute commitment for her to be gone this week?” Why the obsession with Yovanovitch?

Parnas added to the evidence that when it came to Yovanovitch, Trump and his crew willingly allowed themselves to be manipulated by Yuri Lutsenko, a disgraced former chief prosecutor of Ukraine who loathed her for her anti-corruption work. (As the State Department official George Kent said during the impeachment hearings, you can’t fight corruption “without pissing off corrupt people.”) In WhatsApp messages to Parnas, Lutsenko expressed fury that Yovanovitch hadn’t been fired yet. He spoke of all he’d done to push the spurious Biden scandal, adding, “And yet you can’t even get rid of one fool.”

“In that text message to you,” Maddow asked on Thursday, “is Mr. Lutsenko saying, in effect, listen, if you want me to make these Biden allegations, you’re going to have to get rid of this ambassador?” Parnas replied: “Absolutely. Absolutely.”

A few months ago, I wrote a column arguing that when it comes to Ukraine, Trump is at once a con man and a mark, and the information Parnas has provided backs this up. Having promised Lutsenko that he’d get Yovanovitch fired, Parnas told Trump, falsely, that Yovanovitch had bad-mouthed him. His text messages show that he pushed Donald Trump Jr. to tweet about her.

Parnas was the vehicle through which a dirty Ukrainian politician pulled Trump’s strings to take revenge on an American official who’d tried to uphold the rule of law. She was threatened, smeared and fired in part because Trump is easily influenced by the goons and bottom feeders in his orbit.

By going public, Parnas has probably done nothing to sway Republicans toward removing Trump from office, not because they don’t believe him, but because they know Trump did what he’s accused of and don’t care. Writing to Politico’s John F. Harris, a Trump supporter recently described the president as “our O.J.,” an apt analogy for Republicans’ vengeful determination to give a guilty man impunity. (As it happens, Trump will be represented by one of O.J. Simpson’s old lawyers, Alan Dershowitz, at his Senate trial.)