WASHINGTON - The mass shooting at the Pulse nightclub in Orlando two weeks ago has brought out political-anxiety rhetoric in force. Donald Trump, the presumptive Republican presidential nominee, is rocking the electoral world with his raw appeal to fears about terrorism and crime.

His allies in Congress, acting as surrogates, have embraced some of his rhetoric _ questioning likely Democratic candidate Hillary Clinton's commitment to combat Islamic terror _ and demonstrated how fear can enter the political echo chamber and become all-consuming.

Whatever the implications, or morality, of such emotional appeals, politicians have stoked fears since time immemorial and they've done so for a reason: It's often helped them get elected. And it's moved Congress to follow with action.

This year may well prove an exception to the rule. The latest polls show Trump trailing and indicate the public is not embracing his more far-reaching plans for going after terrorists. A new Washington Post-ABC News poll shows as many as 70 percent of voters are anxious about Trump, himself.

Clinton is playing to that fear. Her latest ad hits the businessman for his blase response to Britain's decision to leave the European Union. "In this volatile world," the narrator says, "the last thing we need is a volatile president."

Trump, for his part, has gone all-in.

"We cannot continue to allow thousands upon thousands of people to pour into our country, many of whom have the same thought process as this savage killer," Trump said in his first major speech after the June 12 shooting, reiterating his call for a ban on Muslim immigration.

Of course, the Muslim man who killed at least 49 people in Orlando and injured dozens more was a U.S. citizen born in Queens, N.Y., so an immigration ban would not have applied to him. But Trump piled on anyway, and stoked fears about Clinton.

"She wants to take away Americans' guns and then admit the very people who want to slaughter us," he said.

Some of Trump's biggest supporters in Congress stood by their man.

"It was a good speech. He told the truth about the threat we are facing," said Jeff Sessions, the Alabama Republican who is Trump's top ally in the Senate.

Another Trump surrogate, former House Speaker Newt Gingrich, said Congress should consider reviving a relic of the Red Scare era, the House Un-American Activities Committee, which started in the 1930s as a bulwark against Nazis but eventually oversaw a witch hunt led by Wisconsin senator Joseph McCarthy against alleged communists.

Caryl Rivers, a Boston university journalism professor, said such appeals work particularly well in times of economic uncertainty or when a specific fear is tapped.

"There's always some kind of seed of truth you can pick on," she says. "The fear itself might not be legitimate, but its effect on people is legitimate."

There is, however, the danger of going too far.

"You can scare people so much, it backfires," says Robert Guttman, director of George Mason University's Center for Politics and International Relations.

Many observers believe that Trump has come close to the line repeatedly.

His initial call to ban Muslim immigration came after December's mass shooting in San Bernardino, Calif., by a Muslim couple. He doubled down on the idea after the Orlando shooting, but over the weekend said he would limit the ban to people from countries gripped by terrorism.

He kicked off his campaign last year focused on another sort of immigration, labeling Mexican immigrants "rapists" and "criminals" and vowing to build a wall.

"We don't have a country right now," he says in one of his ads during the primary. "We have people pouring in, they're pouring in, and they're doing tremendous damage."

Clinton, for her part, has stoked fear about Trump and the consequences of his policies.

His demonizing of Muslims would be used by the Islamic State, the jihadist terrorist group, to recruit radicals, she says. His approach to foreign policy could lead to nuclear war. His position on the nation's gun laws would allow terrorists and other criminals to purchase firearms with impunity.

"If the FBI is watching you for a suspected terrorist link, you shouldn't be able to just go buy a gun with no questions asked," she says.

Her allies in Congress, as they fought for new gun legislation with a filibuster and a sit-in in the past two weeks, echoed those calls and accused their colleagues of being complicit in the deaths of innocents.

"We have a Republican who said the problem is not guns. What is the response of the Republicans? More guns, of course," Senate Minority Leader Harry Reid says.

Clinton has made a point of drawing a contrast with Trump. While he pledges to remove fears with force, she suggests replacing them with compassion.

In Clinton's "Brave," ad, she uses a clip from a Nevada event where a young girl tells her, "My parents, they have a letter of deportation. I'm scared for them."

Clinton summons the crying child over to her and says, "I'm going to do everything I can so you don't have to be scared. I'll do all the worrying."

Playing to fears is as old as politics, but changing times dictate changing worries. Yesterday's jitters about communism give way to fears about economic stagnation, violent crime or losing health care.

Even Britain's vote to exit the European Union last week left many Americans unsettled, especially those watching the value of their retirement funds tumble.

Stoking fear has led to political success stories.

In February 1860, Abraham Lincoln said of pro-slavery advocates, "Your purpose, then, plainly stated, is that you will destroy the government, unless you be allowed to construe and enforce the Constitution as you please, on all points in dispute between you and us. You will rule or ruin in all events."

He went on, of course, to win two terms and hold the Union together through the Civil War.

The birthplace of modern political ads arguably dates to the 1964 contest between Democrat Lyndon B. Johnson and Republican Sen. Barry Goldwater of Arizona, when fear mongering met television.

The "Peace, Little Girl," perhaps the most influential political ad ever, juxtaposes a little girl counting the petals she plucks from a flower with the countdown for a nuclear explosion. "These are the stakes," Johnson drawls.

In 1968, Richard Nixon's campaign picked up on a different sort of fear, showing images of the urban unrest and bloodied people in the riots that followed the assassinations of Martin Luther King Jr. and Robert F. Kennedy.

"This time vote like your whole world depended on it." Nixon says at the end of the "The First Civil Right."

In 1988, George Bush famously ran the "Revolving Door" ad that showed a prison with convicts passing through, yes, a revolving door as the narrator described how murderers received weekend furloughs, a program associated with his opponent, Massachusetts Gov. Michael Dukakis.

Social media creates more opportunities.

In an August 2009 Facebook post, former Alaska governor Sarah Palin wrote about a nonexistent "death panel" in Obama's health care plan. Republicans picked up the notion and ran with it as they reclaimed the House majority in 2010.

The 2016 political season's advertising is saturating media airwaves, and a lopsided share of those ads is about national security and terrorism, according to Kantar Media, which tracks advertising trends.

The share of political ads could reach an unprecedented 50 percent of available television advertising air time, particularly in the states with competitive Senate and presidential contests, namely Colorado, Florida, Nevada, New Hampshire, North Carolina, Ohio, Pennsylvania and Wisconsin.

"No other advertiser 'category' has ever claimed or wanted even close to that amount of share; no TV platform has ever wanted to sell anyone else that much," Elizabeth Wilner, Kantar's senior vice president, wrote in a March report.

Despite the success of playing on voter anxiety, there are limits.

"People don't want to feel manipulated, or think they are being pushed around by a message designed to create anxiety," says Shana Kushner Gadarian, an associate professor at Syracuse University.

"Anxiety moves people toward expertise," she says. "When people feel anxious, they really prefer and trust candidates who offer policy solutions and not just threatening language."

McCarthy eventually took his crusade too far, a moment encapsulated when Army counsel Joseph Welch punched back at a hearing and said, "Have you no sense of decency, sir, at long last?"

McCarthy was shortly after censured by his colleagues and his influence evaporated.

Clinton ran up against such limits herself, when she tried to paint her 2008 primary opponent, Barack Obama, as insufficiently experienced to handle crises with her "3 a.m. ad." "That didn't seem to work. I don't think people looked at Barack Obama and said, 'He's a ditz and he's going to make the wrong decision,'" Boston University's Rivers says. "Maybe there were so many other things going for Obama that he didn't play into those fears."

In the most recent phase of the campaign, Clinton, along with Obama, have questioned Trump's temperament .

"She uses it in her own way: Be afraid of Donald Trump. The president did too," George Mason's Guttman says.

But he allows that Trump is a unique case.

"Every time he says something, we think he's gone too far," he says.

Guttman predicts that as the general election heats up, Republicans will concentrate on trying to preserve their House and Senate majorities and begin to shun Trump.

"Many times, Senate races, House races play on scandal, something negative," Guttman says. "But Trump has taken it to a new level."

And that new level will eventually leave him isolated, Guttman believes.

"As we get past the convention and Trump comes into the states, you'll see a lot of people say, 'Oh, I have a previous engagement,'" he says.

Polling has found little public support for Trump's more extreme positions, such as the Muslim ban. But public anxieties about terrorism remain high, especially among Republicans.

About 91 percent of GOP voters believe ISIS is a major threat, while 76 percent of Democrats and independents say so, according to a recent Pew Research Center study. About 85 percent of Trump supporters worry about refugees, compared to 40 percent of Clinton supporter00.

"There's an interplay between candidate and the public _ whether candidates are responding and appealing to the public. But the public is also responding to the candidates," says Jocelyn Kiley, Pew's associate director of research.

For all the criticism of Trump, it's still early.

"There hasn't been the 'Have-you-no-decency moment,'" Rivers says. "Although we're seeing Paul Ryan object, and the president object. It could be we're reaching a critical mass," she continues, before adding, "but we thought we were getting to this point before."