That changed in 2017, when Schiff’s position as the top Democrat on the Intelligence Committee made him a suddenly prominent figure. For the first two years of the Trump presidency, when Republicans controlled the House, the Intelligence Committee was primarily consumed with the tricky task of appearing to investigate Russian interference in the 2016 election while at the same time absolving Trump of participating in — or benefiting from — that interference.

Leading the effort was the committee’s Republican chairman, Representative Devin Nunes. Nunes’s committee Republicans produced a report that concluded that there was no collusion between the Trump campaign and the Russian government; the report further claimed, contrary to the official consensus of the American intelligence community, that the Russian government hadn’t sought to help elect Trump. Nunes also started another set of investigations into the F.B.I. and the Justice Department for what he claimed was “criminal activity and fraudulent behavior” in their investigations of Trump — an unsubtle attempt to undermine Mueller’s efforts.

As the ranking Democrat on the committee, Schiff lacked the ability to single-handedly issue subpoenas or even call witnesses, but he made enterprising use of the little leverage he did have. He appeared frequently on television and held regular news conferences on Capitol Hill, becoming the Democrats’ go-to explainer of what was happening behind closed doors. As the ranking committee member, Schiff was usually allotted unlimited time for an opening statement at the committee’s public hearings — an opportunity members of Congress typically use for grandstanding and speechifying. Schiff thought of the statements as something like the opening arguments he used to make as a prosecutor in Los Angeles courtrooms: an opportunity to zoom out and situate the granular details that juries were about to hear in the bigger picture of the case, focusing their attention on the story he wanted those details to tell.

“We try to set out in sort of non-Beltway language what the general issues are,” Schiff told me, “and why they warrant investigation or warrant concern.” In March 2017, the Intelligence Committee called James Comey, then director of the F.B.I., to testify — the hearing in which Comey revealed for the first time that the F.B.I. had initiated a counterintelligence investigation of Trump’s campaign, Russia and the 2016 election. Schiff’s opening remarks in the hearing arguably established the narrative that governed the Russia story for the next two years. Laying out a timeline of contacts among people in and around the Trump campaign — including Carter Page, Paul Manafort, Roger Stone and others — with Russia and WikiLeaks during the summer of 2016, when Russia’s “active measures” campaign began trying to damage Hillary Clinton and help Trump, Schiff asked: “Is it possible that all of these events and reports are completely unrelated, and nothing more than an entirely unhappy coincidence? Yes, it is possible. But it is also possible, maybe more than possible, that they are not coincidental, not disconnected and not unrelated.”

When Schiff became Intelligence Committee chairman in January, he beefed up the committee’s investigative staff. He hired three former federal prosecutors, a former F.B.I. agent and an investigator who was an expert in Russia-related matters — and who, it happened, grew up in Ukraine and speaks Ukrainian. This summer, the investigator noticed a series of articles in the Ukrainian press about the recall of U.S. Ambassador Marie Yovanovitch and other unusual happenings in U.S.-Ukrainian relations, as well as Giuliani’s comments about Ukraine in the American media. According to another senior Democratic official with the Intelligence Committee, the committee “started developing a potential framework for an investigation” of Trump and Ukraine as far back as June — before the whistle-blower first approached an Intelligence Committee aide, who recommended that the whistle-blower get a lawyer and bring the matter to the attention of an inspector general.

It was the timing of Trump’s supposed wrongdoing, as eventually revealed by the whistle-blower, that was particularly alarming to Schiff and ultimately persuaded him to support an impeachment inquiry. “What struck me was the fact that the president engaged in this conduct” — in his July 25 phone call with Zelensky — “the day after Mueller testified,” Schiff told me. “It demonstrates that this president thinks he’s above the law and there’s no accountability whatsoever. And that, to me, said the greater danger here may be a president who feels completely above the law.”

During his opening statement before Joseph Maguire’s testimony to the Intelligence Committee, Schiff tried to describe “the essence” of Trump’s message to Zelensky during their July 25 phone call. Schiff paraphrased Trump as telling Zelensky, “I want you to make up dirt on my political opponent, understand? Lots of it.” Schiff seemed to be exaggerating for effect, but Trump and other Republicans, in high dudgeon, accused him of fabrication. “Rep. Adam Schiff illegally made up a FAKE & terrible statement, pretended it to be mine as the most important part of my call to the Ukrainian President,” Trump tweeted, “and read it aloud to Congress and the American people.”