(Bastien Inzaurralde/The Washington Post)

The chairman of the House Intelligence Committee was on his way to an event in Washington late Tuesday when the evening’s plans abruptly changed. After taking a brief phone call, Rep. Devin Nunes (R-Calif.) swapped cars and slipped away from his staff, congressional officials said. He appears to have used that unaccounted-for stretch of time to review classified intelligence files brought to his attention by sources he has said he will not name.

The next morning, Nunes stepped up to a set of microphones in the Capitol complex to declare that he had learned that U.S. spy agencies had “incidentally collected information about U.S. citizens involved in the Trump transition.”

Within hours President Trump was declaring that he had been vindicated for his tweets alleging that Trump Tower had been wiretapped by his predecessor, Barack Obama. Public attention on the revelation that the FBI was investigating possible coordination between the Trump campaign and Moscow had shifted to questions about whether Trump officials were victims of spying abuse. And by week’s end, a congressional probe capable of threatening Trump was consumed in partisan fighting and scheduling turmoil.

That sequence was largely engineered by a conservative lawmaker from California’s Central Valley who has emerged as one of Trump’s most tenacious allies on Capitol Hill.

Nunes, 43, has said he is committed to leading an impartial inquiry into Russia’s interference in the 2016 U.S. election, and search for any evidence of coordination with Trump or his associates. But Nunes, who served as an adviser on Trump’s transition team, has also at times used his position as chair of the intelligence committee in ways that seem aligned with the interests of the White House.

House Intelligence Committee Chairman Devin Nunes (R-Calif.) speaks to journalists about an upcoming investigation hearing on Capitol Hill on March 24. (Melina Mara/The Washington Post)

The committee’s course so far has raised concerns about whether it can serve the mission it was given when it was created in the 1970s, putting critical matters of national security above partisan politics.

Former Republican congressman Mike Rogers, who was Nunes’s predecessor as chairman, said that both sides have struggled so far to live up to that historic mandate. “It sows distrust, it shows they don’t have a good working foundation for really hard things,” Rogers said. “Everybody wants to find what they want to find to affirm their political position. That’s no way to run an investigation.”

Last year, Nunes repeatedly skirmished with intelligence leaders over assessments that Russia sought to help Trump win. He has sought to help the White House knock down news stories alleging close ties between Trump associates and the Kremlin. And Nunes has pushed his panel to focus on lines of inquiry — including hunting the sources of damaging news leaks — that seem more favorable to Trump.

Nunes’s latest move came Friday, when he made a flurry of announcements that on the surface signaled promising new investigative paths, including an agreement to hear testimony from Trump’s former campaign chairman, Paul Manafort. But to Democrats, Nunes’s actions again seemed to show the hidden agenda of the White House.

Most immediately, Nunes canceled an open hearing that had been scheduled for Tuesday with former senior officials who have battled Trump. Among them is former acting attorney general Sally Q. Yates, who was fired by Trump; former director of National Intelligence James R. Clapper Jr., who publicly disputed Trump’s wiretapping claim; and former CIA director John Brennan, who has said that Trump should “be ashamed of himself” over his behavior toward U.S. spy agencies.

When Nunes announced the hearing, it appeared that Republicans would use the session to confront the former Obama administration officials over a raft of news leaks. But after the five-hour performance by FBI Director James B. Comey before the committee last week — widely perceived as politically damaging to Trump — GOP members worried about giving Democrats another open hearing to hammer away on Russian interference in the election and any Trump campaign ties to Moscow.

Rep. Adam B. Schiff (D-Calif.), the ranking Democrat on the intelligence committee, said that he suspected the cancellation was driven by “very strong pushback from the White House.”

Schiff also implied he suspects a White House hand in what he called Nunes’s “dead-of-night excursion” to view classified documents. Several congressional officials said they were told about the phone call and swapped cars by members of Nunes’s staff.

Jack Langer, a spokesman for Nunes, disputed the depiction. “That account is inaccurate,” Langer said. He declined to elaborate.

To review classified files without breaking the law, Nunes would have needed to do so at a secure facility. Congressional officials said that the director of National Intelligence, the FBI and National Security Agency had all indicated that they got no late-night visit from Nunes, a trip that probably would have been entered in security logs.

Nunes has repeatedly refused to say where he went or whether the documents were provided by the White House, including when confronted by committee members during a closed-door meeting on Thursday, officials said.

White House spokesman Sean Spicer also refused to rule out a White House role in providing access to the files. “I don’t know where he got the documents from, so I can’t say anything more than ‘I don’t know,’ ” Spicer said during Friday’s White House briefing.

There are clues that such a transaction was coming. Trump said in a recent interview on Fox News that he would “be submitting things before the committee very soon.” And Nunes used his opening statement in the Comey hearing to issue a peculiar request for anonymous sources to bring the committee relevant information.

Arguing the intelligence

Nunes and Trump could hardly have come from more disparate backgrounds.

Nunes grew up among farmers in the flat stretch of fertile land between Fresno and Bakersfield, Calif. He has said that he began buying cattle as a teenager and earned an agriculture degree from Cal Poly San Luis Obispo.

But he showed early ambition and aptitude for politics. After serving on the board of trustees for the community college he had attended, Nunes was elected to the House in 2002. He became a protege of former House speaker John A. Boehner, who tapped Nunes as chairman of the intelligence panel in 2014.

On Capitol Hill, Nunes is known more for his skills as a political operator than his expertise on policy. He can be intemperate and is a fierce protector of allies.

“He is loyal to his friends. And if they’re in a fight, he’s going to be on your side in the fight,” said Rep. Tom Cole (R-Okla.).

That instinct was on display last week when Nunes withheld information about the intelligence reports he had seen from his own committee while rushing to share the information with the White House. The move outraged Democrats and was seen even by some GOP members as a tactical mistake. Nunes apologized the next day.

“Loyalty can sometimes make you, you know, go a step too far,” Cole said. “I’m pretty heartened that [Nunes] recognized that within 24 hours and moved to change it.”

Before the Russia issue, Nunes was mainly known in intelligence circles for his role as an architect of the GOP’s politically charged investigation of terrorist attacks on U.S. facilities in Benghazi, Libya, and his preoccupation with the fate of an obscure U.S. military outpost in the Atlantic Ocean.

That facility, Lajes Field, is a remote U.S. Air Force base in the Azores, wind-swept islands 1,000 miles from Europe. Nunes, a descendant of immigrants from the Azores, waged a lengthy campaign to compel the Pentagon to relocate a major intelligence base in the United Kingdom to the Azores.

Pentagon and U.S. intelligence officials objected, citing prohibitive costs and concerns that civilian employees of the Defense Intelligence Agency — which supplied a large share of the workforce for the U.K. base — would refuse to move there. Nunes responded by inserting a provision in a spending bill that stripped housing allowances for DIA civilians overseas. The language was subsequently removed, but administration officials saw it as a sign of how Nunes operated.

Nunes became an early supporter of Trump and was particularly influential in shaping his national security team. Nunes urged Trump to install retired U.S. Marine Gen. Jim Mattis as defense secretary. For CIA chief, Trump turned to a close Nunes ally from the House committee, Republican congressman Mike Pompeo of Kansas.

Nunes has been at odds with Trump in a few cases, most notably when Nunes said that Trump was simply “wrong” about the claim that Obama had ordered a wiretap of Trump Tower to listen to the Republican presidential candidate. But those differences have been rare and seem not to have jeopardized Nunes’s standing with the president.

Unlike Trump, Nunes is a consistent critic of Russia and Putin. But the chairman has argued with intelligence agencies about their conclusion that Russia’s assault on the presidential campaign — which involved the release of tens of thousands of emails from Democratic Party computer networks — was designed at least in part to help Trump win.

In December, when The Washington Post reported that the CIA had reached that conclusion, Nunes dismissed the finding, saying it was based on “a lot of innuendo, lots of circumstantial evidence, that’s it.”

Nunes went on to suggest that the FBI didn’t agree with the CIA and sought to stage a showdown before the committee. When intelligence officials declined to appear — noting that they were still finishing a final report on the matter — Nunes issued a news release blasting spy agencies for withholding information from Congress. “We want to clarify press reports that the CIA has a new assessment that it has not shared with us,” Nunes said.

The move angered then-CIA Director Brennan, who placed a series of calls to Nunes to remind the chairman that he had been briefed on the latest Russia intelligence. Former officials familiar with the matter said that Nunes did not take Brennan’s calls for nearly two days, speaking to the CIA director only after Nunes had issued his news release.

Brennan went public himself on Dec. 16, saying that the FBI, DNI and CIA were all in agreement on the Russia hacking and its aims. “There is strong consensus among us on the scope, nature and intent of Russian interference,” Brennan said in a public statement.

Langer, Nunes’s spokesman, said Friday, “every element of that account is false.”

When Brennan’s staff sought to arrange a call, Nunes “could not participate in the call immediately because he needed to be in a location where he could access a secure line. The call was then arranged for the following morning,” Langer said.

Adam Entous, Ellen Nakashima and Julie Tate contributed to this report.