WASHINGTON — Richard M. Nixon once said, “People react to fear, not love; they don’t teach that in Sunday school, but it’s true.”
No president since has deployed fear quite like Donald J. Trump. Whether it is the prospect of a crime wave at the border with Mexico or nuclear war with North Korea, President Trump has persuaded his supporters that there is plenty to fear beyond fear itself.
In an interview as a presidential candidate in 2016 with the author Bob Woodward, Mr. Trump said, “Real power is — I don’t even want to use the word — fear.”
As president he tried to intimidate some of the nation’s strongest allies, including Canada, Mexico, Britain, France and Germany, in his initial trade talks. He demanded political loyalty from Republicans in Congress, and drove several who bucked him from office, notably Senators Bob Corker and Jeff Flake. But as his presidency enters its third year, a less convenient truth is emerging: Few outside the Republican Party are afraid of him, and even that intimidation may be changing after the government shutdown.
Mr. Trump has shown little inclination to modulate his style, and that carries risks. He could well face a challenge for the Republican nomination in 2020, and congressional Republicans from swing states could begin to distance themselves from him.
One of the clearest signals came last week when Republicans, backing an amendment offered by Senator Mitch McConnell, Republican of Kentucky and the majority leader, opposed the president’s call for withdrawal of United States military forces from Syria and Afghanistan as part of a Middle East policy bill. Only three Republicans voted against it.
“I believe the threats remain,” Mr. McConnell said in a speech last week. “ISIS and Al Qaeda have yet to be defeated, and American national security interests require continued commitment to our mission there.”
Mr. McConnell also counseled the president last week against declaring a national emergency to get a wall built on the southwestern border even as Mr. Trump emphasized that he was reserving that option.
Even his supporters say the president, who uses the word “tough” as a favored expression of admiration, has not made a measurably effective transition from the world of private business to public office.
“It is a common trait among those who ran privately held corporations,” said Ari Fleischer, who served as White House press secretary for George W. Bush and frequently defends Mr. Trump. “Their way is the only way. Their will gets it done. They’ve been successful against all odds, built something huge, and when they declare it so they expect everybody around them to make it so. That’s Donald Trump’s behavior, and that doesn’t always work in politics or in government.
“Politicians don’t operate the way he does,” Mr. Fleischer said. “Frankly, it’s put him at risk and put the Republican Party at risk, but it also allows him to take on China and do something of tremendous consequences that no politician would ever do. If Trump is successful, this will be a better country and a better world for it.”
Yet there is scant evidence that President Xi Jinping of China, or any other foreign leaders, are cowed.
And certainly not Speaker Nancy Pelosi. The president initially said he felt comfortable negotiating with Ms. Pelosi, but in interviews aired on Sunday sharpened his attacks on her and said her obstinacy on the border wall was damaging the country.
Mr. Trump has found that his lack of experience in politics and diplomacy, which require policy knowledge, team building and nuanced negotiating ability, has left him at a decided disadvantage despite his boasts about his deal-making prowess.
“He’s surrounded in these standoffs by people who have all those boxes checked,” said Timothy O’Brien, the author of “TrumpNation: The Art of Being the Donald.” “Nancy Pelosi has been doing this for quite a while, Putin has been doing this for a quite a while, Xi has been doing this quite a while. They’ve all been running circles around him.”
“The next question is when does he really realize that for what it is, and I think the answer for that is he never will,” Mr. O’Brien said, “because it would admit either defeat or acknowledgment of his inadequacies, and he will just never do that.”
The government shutdown is just the latest and highest-profile example of Mr. Trump sounding assertive but gaining little, at least so far. American allies, diplomats said, have more a sense of resignation than fear in dealing with him. The list of threats from Mr. Trump is long, but the number of times he has followed through is exceedingly short.
“He is playing a role, and the role, much like on ‘The Apprentice,’ was of the strong, able character, but it’s a role,” said David Axelrod, a senior adviser to President Barack Obama. “Every foreign leader and every practicing politician has taken a measure of him and understands the basics, that he responds to strength and there’s not a lot behind the facade.”
In recent months, Mr. Trump has had tense conversations with, among others, Prime Minister Theresa May of Britain and President Emmanuel Macron of France, who has felt trolled by Mr. Trump over the state of the French economy, people familiar with the conversations said.
The German chancellor, Angela Merkel, has indicated to people that she does not consider Mr. Trump a serious person to talk with. His get-tough, tariff-driven approach to bringing China to heel has had mixed results at best, hurting some American industries, and sending markets plunging. Even on one of his most prominent issues where he drew bright lines and promised severe consequences — the renegotiation of the North American Free Trade Agreement with Canada and Mexico — Mr. Trump did not walk away with anything close to a windfall.
Instead, most trade experts said the revised trade accord included modest substantive changes that will benefit the United States, and others said the biggest difference may be symbolic: a change in the name, to the United States-Mexico-Canada Agreement. Congress has yet to vote on that pact.
But there is one place where Mr. Trump’s fear tactics have been an unqualified success: among Republicans. Mr. Trump has held an iron grip on the Republican base, making it difficult for fellow party members, who also rely on those core voters, to oppose him.
“There is no constituency within a party that is so dominated by one individual that is charting a course with the opposition unless you want to be a former lawmaker,” said Josh Holmes, a Republican strategist who is close to Mr. McConnell.
Other presidents have held out the fear of recrimination from the Oval Office to get their way, but they did not use Mr. Trump’s blunt instruments alone.
Lyndon B. Johnson was known for his lean-in, hardball persuasion, but unlike Mr. Trump, Johnson entered a negotiation with an idea of what his opponents wanted, and found a way to get it for them, in exchange for getting what he wanted. Even Nixon later acknowledged that he did not really believe fear was a successful prime motivator.
“Nixon said that, but he didn’t believe it and he didn’t practice it,” said Michael Beschloss, a presidential historian and author of the recent best seller “Presidents of War.” “He actually spent decades building relationships in Washington, with his party leaders, with Democrats, and around the world. So yes, there were certainly elements of fear in all those relationships, but he knew you needed both the carrot and the stick.
“Mr. Trump, given his background as a deal-making real estate developer with close relationships with politicians, might have been expected to do the same in Washington. But among Democrats, he has done the opposite.
“It’s almost as if he only has one tool in his toolbox,” Mr. Beschloss said.