President Trump often stokes the nation’s anxieties in arguing for his agenda. (Washington Post Staff Illustration/The Washington Post)

The machete-wielding man was quickly shot and arrested Friday morning by French police and soldiers, but from the vantage point of 1600 Pennsylvania Avenue, it was a crisis dire enough to put a nation 4,000 miles away on high alert.

“A new radical Islamic terrorist has just attacked in Louvre Museum in Paris. Tourists were locked down. France on edge again. GET SMART U.S.,” President Trump tweeted.

French authorities are indeed investigating the incident as possible terrorism. But other than the critical wounding of the assailant, there were no injuries, except a slight cut to the scalp of a soldier.

Trump’s reaction to the Egyptian attacker who had shouted “God is great” in Arabic also stood in stark contrast to his public silence on the killing of six Muslim worshipers five days earlier at a mosque in Quebec City.

The episode spoke loudly to the fact that stoking fear — a strategy that helped get Trump elected — is emerging as a central part of how he plans to carry out his governing agenda.

People protest outside Trump Tower in Manhattan following President Trump's election victory on Nov. 9. (© Andrew Kelly / Reuters/REUTERS)

“He wants people to understand that he is aggressively going to combat anybody who seeks to do us harm and he’s going to put the safety and security of this country first,” White House press secretary Sean Spicer said. “He’s not going to sugarcoat it.”

That is a theme to which Trump has returned again and again at critical moments — from his acceptance speech at the Republican National Convention that conjured “crime and terrorism and lawlessness,“ to his dark inaugural address, with its vivid image of “American carnage.”

Channeling and amplifying fear can be an effective campaign tool, but Trump’s critics say it is a dangerous way to lead a country.

“It is used to increase the public threshold for risk,” said Michael Gerson, a chief speechwriter for former president George W. Bush who writes an opinion column for The Washington Post. “Because poor neighborhoods can’t get any worse, why not try something new? Because America is already a jihadist battleground, why not take a radical and discriminatory new direction on immigration? Because the planet is in chaos, why not entirely reorient American foreign policy toward alliances and great power rivals?

“Things, after all, can’t get any worse,” Gerson continued. “The problem is: Things can get a lot worse, and quickly.”

Playing upon the nation’s anxieties about what might happen also stands as a stark contrast to how presidents have lifted the country out of actual crisis in the past.

Officers patrol the courtyard of the Louvre museum near where a soldier opened fire on a machete-wielding attacker on Friday. (Christophe Ena/AP)

Perhaps most famous was the line that most Americans can still recite from Franklin D. Roosevelt’s first inaugural address, when he told a country in the depth of the Great Depression that “the only thing we have to fear is fear itself — nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance.”

There were also other presidents — Bill Clinton in the wake of the 1995 bombing of a federal building in Oklahoma City, Bush standing on the rubble of the World Trade Center in 2001 — who seemed to grow into the job as they summoned the nation to defy what it feared rather than succumb to it.

Scholars of the subject say they can think of no previous U.S. president so enamored as Trump with scare tactics.

“If he frightens people, it puts him in the driver’s seat. He’s in control,” said historian Robert Dallek. “These are what I think can be described as demagogic tendencies.”

Timothy Naftali, a New York University professor who specializes in presidential and national security history, said, “We have a special word for seeing a threat everywhere. It’s called ‘paranoia.’ It’s good for mobilizing a base. It’s very bad for turning a base into a governing majority.”

One danger, Naftali said, is that “a fatigue” will settle in, making people numb and skeptical when actual threats emerge.

Trump’s penchant for amplifying potential threats on the campaign trail drew sharp rebukes from then-President Barack Obama, who warned repeatedly that he was misleading the public by exaggerating the danger posed by terror groups such as the Islamic State.

“Groups like ISIL can’t destroy us, they can’t defeat us,” Obama said, using an acronym for the group last March during a trip to Argentina. “They don’t produce anything. They’re not an existential threat to us. They are vicious killers and murderers who perverted one of the world’s great religions. And their primary power, in addition to killing innocent lives, is to strike fear in our societies, to disrupt our societies, so that the effect cascades from an explosion or an attack by a semiautomatic rifle.”

Obama — like Bush before him — had been careful not to use the phrase “radical Islamic terrorism,” saying the phrase would aid terror groups intent on casting the United States in a war against Islam. Trump has made a point of embracing the term.

Julie Smith, a former national security aide in the Obama administration, said that every administration must balance the need to level with the public about actual risks and to also reassure them to avoid causing an overreaction or panic.

“Trump is determined to instill fear at every turn in order to put faith in whatever idea he comes up with about making Americans safer,” she said. “These guys don’t talk in nuance. They talk in stark terms, in black and white, about fighting the bad guys.”

For years, the public was weary of war in places such as Iraq and Afghanistan and leery of U.S. military overreach in those regions, Smith said. But after the Obama administration’s struggles to respond to the civil war in Syria, and the gruesome images of the Islamic State beheading American hostages, the public grew more fearful.

“Many Americans, polling data shows, are of the mind that ISIL is, in fact, an existential threat,” Smith said, “when in reality, they are a very serious threat that we must do everything we can to combat. But they are not in position to fundamentally bring down the United States.”

Ian Bremmer, president of the Eurasia Group, a global risk analysis firm, faulted Obama for his “unwillingness to portray radical Islam as a problem, when globally it was an issue.”

But Trump, Bremmer said, has “gone way too far in the other direction.”

On Sunday, Trump wrote in a Twitter message: “Our country needs strong borders and extreme vetting, NOW. Look what is happening all over Europe and, indeed, the world — a horrible mess!”

Bremmer said Trump failed to differentiate that the United States has been far more effective in integrating immigrants and refugees than Europe has been. Trump’s rhetoric risks alienating Muslims in the United States who might be less trustful of cooperating with U.S. authorities to help root out terror plots or other risks.

On the flip side, Bremmer said, Trump’s approach is “a great strategy for the base.”

“There are a lot of white, undereducated men in America who see the world become less white and less undereducated and less male who have a problem with that,” Bremmer said. “Trump speaks very clearly to them. He’s willing to brand ‘the other.’ He’s doing it with China and Mexico and he’s doing it with terrorism, and he’s doing it very effectively.”

Chris Newman, an immigrant rights advocate with the National Day Laborer Organizing Network, said Trump has purposely blurred the lines of various potential threats to the country, including undocumented immigrants living here, refugees from abroad and even the unfounded claims that up to 5 million immigrants voted illegally in the presidential election.

“He lumps them altogether to stoke fear,” Newman said. “Our view is that President Trump is engaged in a salesman, carnival trick — he’s selling fear first and then selling the fact that he can respond to the fear — only he can fix it.”