The world spins faster these days, but in Washington, as President Trump is now learning, the essential chemistry of crisis — quick to boil, difficult to dampen — hasn’t changed in four decades.

Tom Railsback, one of the last surviving members of the House Judiciary Committee that voted to impeach Richard M. Nixon, recalls the moment he knew he and his party finally had to break with their wayward president. “I personally liked Richard Nixon,” said Railsback, a Republican from Illinois who is now 85. “He campaigned for me. But I reached a point — a number of us did — where we all felt that this was the most important decision of our lives.”

No such decision confronts ­Republicans in Congress or the administration right now, but within the president’s party this week, what had been a fairly solid wall of support has suddenly developed cracks — the latest being the appointment late Wednesday of a special counsel to investigate Russia’s role in Trump’s election. Are those cracks dangerous splits in the foundation of Trump’s support or merely cosmetic chinks that might be patched by, say, a successful presidential trip to Europe and the Middle East?

“The danger he faces is his own party, with a growing chorus of leading Republicans who want to distance themselves from Trump because he has the smell of a wounded animal,” said Douglas Brinkley, a presidential historian who met with the president-elect at the Mar-a-Lago Club in Palm Beach, Fla., in December as Trump prepared to take office. “Right now, there aren’t many Republicans in Congress facing reelection who are going to want to be in photo opportunities with him. He’s a man without coattails.”

[Lawmakers demand FBI, White House hand over records.]

(Peter Stevenson,Jason Aldag,Whitney Leaming/The Washington Post)

Rep. Mike Simpson (R-Idaho) is old enough to recall watching Republicans turn against Nixon in the latter phases of the Watergate investigation. “What I’m worried about is, in the early 1970s, politicians like me were standing around saying, ‘Nixon’s okay; he didn’t do anything,’ and look what it led to,” said Simpson, who was in dental school as the Nixon presidency crumbled.

Now, with revelations dominating the news almost daily, “you find Republican politicians kind of a little leery about saying either they support Trump or ‘Oh, no, this is all made-up, fake news bulls--- stuff,” Simpson said. “They’ve seen what’s happened in the past, and as long as this continues, it’s hard to stand behind him, I’ll tell you in all honesty.”

But where some see the start of a snowballing opposition, others caution that a momentary crisis does not necessarily imply collapse.

“I see the parallels with Watergate, but the differences are enormous,” said David Greenberg, a historian at Rutgers University who has written books on Nixon and the politics of media coverage. “We are so far from the mountain of evidence we had in the spring of 1973. Some Republicans feel it’s imperative now to furrow their brows about Trump’s behavior, but for the most part, they are still very much on board with him. We’re in the early stages, certainly not the endgame.”

[Rosenstein’s Senate appearance Thursday will be a big moment for him — and for Trump]

In the Watergate scandal, hard evidence — including the burglary at the Democratic National Committee headquarters and the discovery of Nixon’s White House taping system — as well as convictions of some of the president’s aides made it easier for Republicans to break with their president, Railsback said. He does not think that the crisis that has engulfed the Trump presidency has reached that point, but he viscerally recalls the feeling of collapsing confidence that led him and his fellow Republicans to discard core beliefs about loyalty and party discipline.

“It was easier then because things were a lot more nonpartisan, and in those days I had very good friends that were Democrats,” he said. “But there came a point when both parties had to tone down the rhetoric and look for the common good.”

(Thomas Johnson/The Washington Post)

On Capitol Hill and in the conservative media Wednesday, by word and by gesture, Republicans edged away from the president whose world-shaking election last fall had put them where they’d dreamed of being since 2007 — in charge of the whole kit and caboodle in Washington, finally in position to turn their ideas into action.

But after a whirlwind first hundred days of china-breaking rhetoric and frustratingly stalled progress on Trump’s biggest initiatives, this new presidency has become mired in the mud of scandal: The firing of the FBI director, who was leading an investigation into any role Russia may have played in Trump’s election. The president’s decision to share classified information with Russian officials. A report that Trump had asked FBI chief James B. Comey whether he might shut down an investigation into Trump’s former national security adviser, Michael Flynn. Then, on Wednesday, the Justice Department announced the appointment of a special counsel, heightening the sense of an administration under siege.

[Special counsel appointed to oversee probe of alleged Russian interference in 2016 election.]

Republicans in Congress moved from ritual statements of solidarity to worries about Trump’s “troubling” behavior, and from assurances that the process was working to outright calls for independent investigations of the president’s actions. But only two Republicans joined with 197 House Democrats to sponsor a bill that would have created a commission to look into suspected Russian interference in the 2016 election; GOP lawmakers on Wednesday blocked a vote on the bill. Still, Republican leaders of committees in both chambers of Congress demanded that the White House produce documents and any tapes, if recordings exist, that might shed light on reports that Trump pressed Comey to halt his investigation.

Sometimes, silence spelled out the shift in Republican support for the president. Senate Majority Leader Mitch McConnell (R-Ky.) ignored questions from reporters about the controversies. On Fox News, where Republican lawmakers are most comfortable speaking to their base, anchor Bret Baier on Tuesday night told viewers that he had found no one to defend the president. “We’ve tried tonight to get Republicans to come out and talk to us, and there are not Republicans willing to go on camera tonight,” he said. “This story changed the dynamic on Capitol Hill.”

Current politicians, as well as those who served during the Nixon and Bill Clinton impeachment processes, said they based their decisions about a president’s ability to serve on some combination of public opinion, consensus among political and media voices, and their own moral compasses.

Although his constituents are not following every twist in the D.C. drama, Rep. Carlos Curbelo (R-Fla.) said: “I do think it’s taking a toll on the psyche of our country. You know, this constant dose of scandal, of controversy, of intrigue, it’s just not healthy. What it does is it erodes the trust and confidence in our institutions.”

Curbelo, whose South Florida district voted for Hillary Clinton for president by a wide margin, said he has decided to make public the discussion of impeachment that has become commonplace in private chatter on the Hill.

“If any congressional committee documents and concludes that any federal official is guilty of obstruction of justice,” he said, “certainly that would rise to the level of impeachment. . . . I don’t think that’s what will likely end up happening. But is it something that’s on people’s minds around here? Yes. I happen to be saying it publicly; most members are saying it privately.”

After Rep. Jason Chaffetz (R-Utah), chairman of the House Oversight Committee, announced an inquiry into the Trump-Comey meeting, he said, “I had a number of members send me a personal text saying, ‘Thank you, good job, keep it up. Glad we’re out there, not ducking this.’ ”

Chaffetz said his party’s credibility is at stake. “The public is really good at sensing authenticity,” he said. “If we fall anywhere short of being thorough, responsible and complete in our investigation, the public will get it and they’ll get rid of us.”

Although Trump’s approval ratings are historically low for a new president, they remain well above the depths that Nixon and George W. Bush experienced at the nadirs of their presidencies. “The thing that would make these cracks really widen would be hard evidence directly linking Trump or top aides to Russia, or showing a deliberate plan to snuff out the investigation,” Greenberg said.

“I don’t think this has reached the point for an impeachment inquiry, but both parties have to move quickly to complete a careful investigation,” Railsback said. “It’s overheated now — some of that has been brought on by the president, but the media has been overly aggressive and too speculative.”

Trump loyalists — and the president himself — have sought to paint the snowballing media coverage of the Comey memo and Trump’s disclosures of classified information to Russian officials as evidence of a partisan, anti-Trump bias.

“Look at the way I’ve been treated lately, especially by the media,” the president said during his commencement address Wednesday at the U.S. Coast Guard Academy in New London, Conn. “No politician in history — and I say this with great surety — has been treated worse or more unfairly.”

Presidents have faced the ultimate sanction mainly when there was bipartisan consensus that they had lost the trust of the nation. “With Watergate,” Greenberg said, “from fairly early on, there were at least some Republican voices that were critical, and that shaped public opinion. With the Clinton impeachment, it was very hard to argue at any point that this was anything other than partisan. Until you have that bipartisanship, talk of impeachment is wishful thinking by Democrats.”

At this early stage in the Trump presidency, there is still ample opportunity to build support, Brinkley said. “He could do a prime-time address to the American people like Ronald Reagan did in the Iran-contra crisis,” the historian said. “He still has a core base of supporters, but he hasn’t sought to unite Americans beyond his base.”

For decades, Trump has boasted that he thrives along the edges of failure, that he and risk are the most comfortable of bedfellows.

At the Coast Guard Academy on Wednesday, Trump told the graduates that they will face rough passages, just as he is facing today. “Never, ever, ever give up,” he said. “Things will work out just fine.”

Thirty years ago, as he was amassing his first fortune, Trump explained why he had such a voracious appetite for properties and publicity: “I do it to do it,” he wrote in his bestseller, “Trump: The Art of the Deal.” “But in the end, you’re measured not by how much you undertake, but by what you finally accomplish.”

In that same book, however, Trump — always brimming with confidence that he can land any deal, vanquish any rival — made one concession. “Making choices,” he wrote by way of explaining why he would rather run his own company than take his business public, “is a lot easier when you have to answer only to yourself.”

Mike DeBonis, Paul Kane and Carol D. Leonnig contributed to this report.