The lobby of CIA headquarters in Langley, Va. (Larry Downing/Reuters)

The election results were only hours old Wednesday when a sober team of intelligence analysts carrying black satchels and secure communications gear began preparing to give President-elect Donald Trump his first unfiltered look at the nation’s secrets.

The initial presentation — to be delivered as early as Thursday — is likely to be a read-through of the President’s Daily Brief, the same highly classified summary of security developments delivered every day to President Obama. After that, U.S. intelligence officials are expected to schedule a series of meetings to apprise Trump of covert CIA operations against terrorist groups, the intercepted communications of world leaders, and satellite photos of nuclear installations in North Korea.

The sessions are designed to bring a new president up to speed on what the nation’s spy agencies know and do. But with Trump, the meetings are likely to be tense encounters between wary intelligence professionals and a newly minted president-elect who has demonstrated abundant disdain for their work.

A palpable sense of dread settled on the intelligence community Wednesday as Hillary Clinton, the candidate many expected to win, conceded the race to a GOP upstart who has dismissed U.S. spy agencies’ views on Russia and Syria, and even threatened to order the CIA to resume the use of interrogation methods condemned as torture.

“It’s fear of the unknown,” said a senior U.S. national security official. “We don’t know what he’s really like under all the talk. . . . How will that play out over the next four years or even the next few months? I don’t know if there is going to be a tidal wave of departures of people who were going to stay around to help Hillary’s team but are now going to be, ‘I’m out of here.’ ”

“I’m half dreading, half holding my breath going to work today,” said the official, who, like others, spoke on the condition of anonymity, citing the sensitivity of the subject.

Michael Hayden, the retired Air Force general and former CIA director who in 2008 briefed a highly skeptical President-elect Obama on the agency’s counterterrorism operations, said that intelligence officials are likely to approach their initial meetings with Trump with professionalism, but also consternation.

“I cannot remember another president-elect who has been so dismissive of intelligence received during a campaign or so suspicious of the quality and honesty of the intelligence he was about to receive,” Hayden said in a telephone interview Wednesday. The initial meetings with Trump in the coming weeks are likely to be professionally conducted, he said, but characterized by “a little caution, a little concern.”

Trump has already received at least two preliminary briefings, arranged during the campaign by Director of National Intelligence James R. Clapper Jr. But those were done out of tradition and courtesy, providing both candidates broad overviews of security issues while holding back secrets about drone strikes, eavesdropping capabilities and other covert programs.

Intelligence officials were deeply troubled early in the campaign when Trump declared that he might be inclined to instruct the CIA to resume operations to capture terrorism suspects and subject them to brutal interrogation measures, including waterboarding. That agency program was dismantled in 2009, and measures passed since then would make its resumption illegal.

In China, Russia and Israel, we ask people what they think of the election of Donald J. Trump as the 45th president of the United States. We’ll update this video as more voices come in. (Jason Aldag/The Washington Post)

Trump subsequently backed away from those comments, which were interpreted by some as empty saber-rattling.

“He could revive a program of secret prisons” overseas, said John Rizzo, former acting general counsel of the CIA, but would be likely to find it difficult to get any foreign country to agree to host one.

His other problem would be convincing the workforce at the CIA to carry out his wishes. “There would be such pushback,” said Rizzo, whose confirmation as general counsel was derailed because of his participation in crafting the so-called enhanced interrogation techniques used on al-Qaeda suspects in the early 2000s. “Given what it cost the agency” in terms of reputation, “there would be extremely strong resistance,” he said.

More recently, U.S. intelligence officials have been disturbed by Trump’s positions on Russia — his statements encouraging Moscow to seek to steal Clinton’s emails and his refusal to accept the intelligence community’s conclusion that the Kremlin was behind a cyberespionage campaign targeting Clinton and the Democratic Party.

That finding was presented to Trump in one of his early intelligence briefings and then reinforced last month when Clapper’s office took the rare step of issuing a public statement declaring Russia complicit in the hacks.

Trump treated that determination as unfounded rumor. “I don’t know if they’re behind it, and I think it’s public relations, frankly,” Trump said last month.

Trump has vowed to obliterate terrorist groups including the Islamic State but has offered few specifics on how he would deploy the principal entities in that fight: the CIA and the military’s elite Joint Special Operations Command.

The Obama administration spent years developing guidelines for counterterrorism operations, requiring multiagency approval on most drone-strike targets and “near certainty” that no civilians would be harmed.

That “playbook” is spelled out in presidential orders that will remain in effect unless Trump specifically moves to scrap them, administration officials said. Trump could rescind the procedures or issue his own orders setting out revised rules governing the use of drones and commando teams. But officials said a decision to throw out the Obama playbook risks sparking backlash from career professionals at the Pentagon and the CIA who have been implementing the rules since they were put in place.

The absence of seasoned national security officials on Trump’s campaign staff has been a source of concern at the CIA, the Pentagon and other agencies. His most prominent adviser with intelligence-related credentials is retired U.S. Army Lt. Gen. Michael Flynn, who was forced out of his job as director of the Defense Intelligence Agency and dined with Russian President Vladi­mir Putin last year.

Speculation on where Flynn and former New York mayor Rudolph W. Giuliani might serve in a Trump administration added to the unease among national security officials Wednesday. “Is Giuliani going to be our attorney general?” one official asked.

Some officials drew comparisons to earlier eras — including the administration of Richard Nixon — that were characterized by White House hostility toward key departments and agencies, noting that the Justice Department, Pentagon and CIA survived.

What Trump has said about the CIA and the military has “put us in a difficult position, but the flip side is there is an institutional ability to survive,” said a second senior U.S. official. “Bureaucracies chug along and take lumps and have conflicts. If you ask about rank and file, for a long time there has been a sense that [presidents and administrations] come and go, but we’re still here. You’ve got to assume that the Foreign Service at State, generals at the Department of Defense have that belief. There’s an institutional stability built into the system that can withstand spasms.”

Dana Priest and Adam Entous contributed to this report.