Susan Glasser explained in the New Yorker why the testimony of Ambassador Marie Yovanovitch was so powerful:

For a few hours on Friday, an unassuming career diplomat named Marie (Masha) Yovanovitch did something that I thought had become impossible in Donald Trump’s Washington: she managed to hold on to her amazement and outrage at the President’s amazing and outrageous actions. In this hyper-partisan, hyper-political time, she was neither. Nearly three years into this Presidency, that is no given. A state of weary cynicism has taken hold regarding Trump, among his supporters and also his critics. He is what he is. What can we do about it? Even impeachment has quickly come to be seen through this lens. Members of Congress are all too likely to vote the party line. Does any of it matter?

In hours of spellbinding testimony, on the second day of the House’s public impeachment hearings, Yovanovitch offered a decisive rebuttal to that way of thinking. She said that she had been surprised and appalled when Trump succumbed to a foreign disinformation campaign and fired her as the U.S. Ambassador to Ukraine based on false allegations trafficked by Rudy Giuliani, his private lawyer. She had taken on corrupt interests inside Ukraine, and those parties had, in turn, targeted her—and, unbelievably, it had worked. The President, the most powerful man in the world, had gone along with it. “It was terrible,” she said. Yovanovitch said that she was shocked when Secretary of State Mike Pompeo failed to issue a statement in her defense, although she had spent thirty-three years in the Foreign Service. She said that she was intimidated and incredulous when the President attacked her in a phone call with a foreign leader. She said that she felt threatened. These are simple truths, which is why they were so powerful. So was the question she posed to the members of the House Intelligence Committee arrayed on the dais in front of her: “How could our system fail like this?” That, of course, is a question for which Americans as yet have no real answer.

As with most truly memorable public moments, there was something raw and unexpected about Yovanovitch’s appearance on Friday; it cut through the rote posturing and partisanship to get at an essential fact. Yovanovitch reminded us that all of this is, in fact, amazing and shocking and outrageous. It is not normal. Trump is not on the brink of impeachment because of some arcane dispute over differing philosophies about anti-corruption policies in Ukraine. Yovanovitch, who spent her career fighting corruption in the former Soviet Union, was dumped because the President had allied himself with Ukrainians who wanted to stop America’s anti-corruption efforts. He personally ordered her fired. He spoke threateningly of her during a phone call with Ukraine’s new President and did it again, on Twitter, while she was testifying on Capitol Hill. No previous President—of either party—has ever acted in this way.

That is why Yovanovitch’s appearance was ultimately about what the hell the country is supposed to do with a President who is so manifestly unpresidential. Friday offered a chance to reflect on Trump’s conduct, to consider the extent of his boorishness, his poor judgment, his ignorance, his recklessness, and his callous disregard for anything other than his own personal interests. There will be many days and weeks to come in which to hash out what, if anything, in all this saga involving Ukraine, should be considered impeachable by Congress. But that is not the real import of Friday’s hearing, which was a rare opportunity for America to stop and take stock of Trump and what he has wrought. This was a day to contemplate the excesses of Donald John Trump…

For hours, she did not waver or change her demeanor. She was sincere and corny and old-fashioned in her insistence on the values that politicians often talk about but, in the Trump era, have more or less jettisoned. There was a moment when Yovanovitch reminded the committee about the oath that members of the Foreign Service swear to the Constitution. “We take our oath seriously—the same oath that each one of you takes,” she told the panel, looking directly at the dais where Nunes had just opened the session by speaking once again about a bizarre alleged plot by Democrats to obtain “nude pictures of Trump.” Earnestness, as Yovanovitch showed, is not entirely dead in American public life.

Several times, Yovanovitch was asked why it mattered that Trump had fired her, what his prerogative was, and why we should care about it. She reached back to the Truman era and to Arthur Vandenberg, the late Republican senator from Michigan, a prewar isolationist who became a pillar of the postwar internationalism that had been the hallmark of American foreign policy right up until Trump took office. “Partisan politics stops at the water’s edge,” Vandenberg was famous for saying, even if the two parties were never as bipartisan about foreign policy as his statement implied. At least the aspiration was there, even if the execution faltered. Yovanovitch still seemed to want to believe it. She insisted upon the idea that there remains an American national interest, as opposed to a Republican interest, a Democratic interest, or a Presidential interest. She was an Ambassador from our past, and maybe from our future. But not, sadly, from our present.