Republican presidential candidate Donald Trump, left, looks on as a Trump supporter reaches for a sign that reads "Islamophobia is not the answer" at a rally in Oklahoma City on Friday. (Sue Ogrocki/AP)

At a rally in southwest Virginia on Monday, Republican front-runner Donald Trump again told an apocryphal story about a general killing Muslim terrorists with bullets dipped in pigs’ blood. In Tennessee on Saturday, he promised to bar Syrians from the country “until we find out what the hell is going on.” In Oklahoma City the night before, he launched into a passionate defense of waterboarding after a protester flashed a sign reading “Islamophobia is not the answer.”

And every time, the crowd roared with deafening cheers.

Along with his attacks on illegal immigrants, Trump’s willingness to go further than any of his GOP rivals in casting suspicions on Muslims has horrified many Republican establishment figures and has attracted widespread condemnation from both parties.

But for many Trump supporters, the GOP front-runner’s harsh rhetoric on Muslims is one of the keys to his appeal, especially among evangelicals who feel that Christians are under siege and hampered by political correctness. Those feelings are probably a big part of the reason Trump is leading most of the 11 primary contests being held Tuesday, especially those in the South.

“Mr. Trump is not against Muslims. . . . Not all Muslims are bad, but ISIS, they are Muslims, so I have to think we have to group them together now,” said Charlie Shane, 21, a junior at Texas Tech University who decided to vote for Trump when he promised to bomb the Islamic State, also known as ISIS and ISIL.“He’s trying to keep Americans safe. Our lives are more important than theirs, and that’s just the reality.”

A man listens as Republican presidential candidate Donald Trump speaks during a campaign event in Madison, Ala., on Sunday. (Jabin Botsford/The Washington Post)

Trump has not only promised to “bomb the s--- out of ISIS” — he would also kill the loved ones of suspected jihadists. He would bring back waterboarding — which is forbidden by U.S. and international law but which Trump considers “minimal, minimal, minimal torture” — and would do “much worse” to suspected terrorists. He would temporarily ban most foreign Muslims from entering the country and would heavily surveil and possibly close some U.S. mosques.

“I think we need to, because that’s where it’s coming from,” said Jan Osban, 68, a retired nurse who attended Trump’s rally in Oklahoma City on Friday and plans to vote for him. “They use a religion to justify killing people. . . . They’re so insidious that they can be right here and you don’t know it until too late.”

The Muslim American community has been rushing to combat such statements, often with the help of interfaith partners. But they are struggling to match the wave of fear that has consumed much of the Republican base.

“The American Muslim community has never felt this level of apprehension and fear,” said Ibrahim Hooper, spokesman for the Council on American-Islamic Relations. “It really is open season, rhetorically, on American Muslims and Islam.”

Newt Livesay, a 73-year-old veteran and custom-knife maker who attended Trump’s rally in northwest Arkansas on Saturday afternoon and plans to vote for him in Tuesday’s primary there, said he has known many Muslims over the years, including his doctor, who is “as nice and as good a doctor as I’ve ever had.” But he distrusts Muslims living in the Middle East who could have ties to the Islamic State.

“Somebody said, ‘Well, we ought to make them our friend,’ ” Livesay said. “No, we need to make these people fear us.”

Trump speaks during a campaign watch party on the day of the Nevada Republican caucus in Las Vegas last Tuesday. (Jabin Botsford/The Washington Post)

Early in Trump’s candidacy, much of his most incendiary rhetoric focused on illegal immigrants, whom he described as violent criminals that he would kick out of the country and keep at bay with a massive wall along the southern border. He only tested the waters with comments about Muslims, sometimes coyly suggesting that President Obama is Muslim rather than Christian.

But his tenor changed and hardened as Europe grappled with the sudden influx of millions of Syrian refugees, most of them Muslim, fleeing a violent war in their homeland. Democratic candidates called on the United States to accept thousands more refugees, while most Republican candidates, including Trump, said the United States is not equipped to take on any more.

At a Trump rally in New Hampshire in late September, a man in the crowd bellowed: “We have a problem in this country — it’s called Muslims!” The man then called the president a Muslim and warned of Muslim training camps. Trump laughed off the comments as the crowd clapped.

Two weeks later at another rally in New Hampshire, Trump declared that as president he would kick all Syrian refugees out of the country and bar any more from entering, saying they could be a secret terrorist army. That provided some of his loudest applause of the night.

In November, Trump repeatedly promised to bomb the Islamic State. Then came the Paris terrorist attacks and the mass shooting in San Bernardino, Calif., both of which were tied to the Islamic State. Trump called for greater scrutiny of mosques and newly arrived Muslims, along with urging the United States to kill the relatives and loved ones of terrorists.

Finally in early December, Trump called for a “total and complete shutdown of Muslims entering the United States until our country’s representatives can figure out what is going on.”

The idea was quickly denounced by the party establishment — and embraced by many Republican voters. Nearly 60 percent of Republicans supported the proposal, according to a Washington Post-ABC News poll conducted in December. Exit polls from recent primaries have shown similar levels of support.

On the night before the South Carolina primary, Trump held a rally in North Charleston and told a story to illustrate his support of waterboarding: U.S. Gen. John J. Pershing once captured 50 terrorists, dipped 50 bullets in pigs’ blood, then shot 49 of the terrorists, sending one home to warn others.

Historians have found no evidence that this event occurred, and many Muslim Americans have denounced its message. Nonetheless, Trump repeated the story Monday in Virginia.

During the South Carolina primary, held on the same day as Supreme Court Justice Antonin Scalia’s funeral, Trump tweeted: “I wonder if President Obama would have attended the funeral of Justice Scalia if it were held in a Mosque?”

Trump decisively won in South Carolina, and exit polling found that three-quarters of Republican voters there supported a temporary ban on Muslims entering the country.

Many self-described evangelicals seem particularly open to Trump’s rhetoric about Muslims. He promises to protect Christianity and turn the United States into a place where shop clerks wish you a “Merry Christmas,” and his rallies always open with a prayer. At a rally in Myrtle Beach, S.C., in February, local evangelical pastor Mark Burns mentioned Democratic presidential candidate Bernie Sanders, who is Jewish, and then said, “You’re going to make sure we elect a man who believes in the name of Jesus Christ.”

At a rally in southern Georgia on Monday night, Trump told a screaming crowd of several thousand that Christians and evangelicals should have more political power.

“Why is it that we get pushed around? For instance, I made the statement about Muslims,” Trump said, adding that he respects the religion and has friends who practice. “But there’s something going wrong here, folks. And I said: We have to do something temporarily. We have to find out what’s going wrong. We can’t let the Syrians come in.”

A Pew Research Center survey in 2014 used a “feeling thermometer” to measure how various Americans feel about Muslims, and white evangelical Christian reported having the coolest feelings. Many evangelicals also feel under siege in a fast-evolving culture where gay marriage is now legal and non-Christian holidays are added to some school calendars.

“We’re being attacked. We are literally being attacked,” said Linda Barnett, 67, a Trump supporter from Moore, Okla., who works for a ministry group and has long been skeptical of Islam. She is encouraged by Trump’s approach.

“I totally agree with him,” Barnett said. “The ones that are already over here, they say, ‘We’re peace-loving people.’ I’m sorry, I’m sorry — if they believe in the Koran, there is nothing peace-loving about them, because the Koran is not peace-loving. The Koran is to destroy everybody that is not Muslim. . . . So if they throw a fit about us watching them and following them around, well then go back to where you’re supposed to live.”

Barnett attended Trump’s rally Friday night in Oklahoma City. As Trump warned of “the migration,” a young man sitting behind him held up a sign reading “Islamophobia is not the answer.”

The crowd erupted in anger. Another young man grabbed the sign, crumpled it and triumphantly waved it over his head. Another ripped it to pieces while Trump stopped speaking and turned around to watch. As police escorted the protester away, the crowd chanted: “Trump! Trump! Trump!”

“You see, in the good old days, law enforcement acted a lot quicker than this. A lot quicker. In the good old days, they’d rip him out of that seat so fast — but today, everybody’s politically correct,” Trump said, adding that police are afraid to do their jobs. “Our country’s going to hell with being politically correct. Going to hell.”

Police should not be afraid to properly do their jobs, he said, just like U.S. interrogators should not hesitate to waterboard suspected terrorists.

“We are really becoming a frightened country,” Trump said, “and it’s very, very sad.”

Michelle Boorstein, Scott Clement and Sarah Pulliam Bailey contributed to this report.