Scenes of masked men toting guns and waving black Islamic State flags. Refugees scrambling across the border. Fires and explosions.

It’s not just a Donald Trump ad. Most of the Republican presidential contenders and their allies are now waging campaigns focused on fear — bombarding voters with ominous television spots that warn of national security threats and amping up their alarming rhetoric on the stump.

The commercials saturating the airwaves in Iowa and New Hampshire reflect how worries about terrorism are crowding out domestic issues such as tax policy and health care among GOP voters. The candidates are scrambling to outmuscle one another, offering dark assessments of the Obama administration’s fight against violent extremists and warning that their rivals are ill-equipped to take up the cause.

“It is time for us to open our eyes and not to think about the world as we wish it was, but to deal with the world as we see it is,” New Jersey Gov. Chris Christie told about 250 voters gathered at an Italian restaurant in Manchester, N.H., on Monday. “And it is a dark and dangerous place right now. In every corner that we look.”

Former Florida governor Jeb Bush delivers a similar message in a TV spot that begins airing in New Hampshire this week. “We are at war with radical Islamic terrorism,” he declares. “We have but one choice: to defeat it.”

New Jersey Gov. Chris Christie, shown campaigning in New Hampshire on Sunday, says the world is a “dark and dangerous place.” GOP candidates are amping up their ominous rhetoric as the primaries near. (Katherine Taylor/Reuters)

And in Iowa, a new ad by super PACs supporting Sen. Ted Cruz (Tex.) features a frightening montage of Islamic State militants, refugees on the run and rolling tanks before mocking Sen. Marco Rubio (Fla.) as a lightweight.

[Cruz super PACs portray Rubio as a distracted fantasy-football devotee]

The deluge underscores the unconventional nature of the crowded Republican primary fight, one that has been dominated by Trump’s provocative exhortations portraying America as under siege. Even disengaged voters are being enveloped in warnings that the country is losing the battle against terrorism, just as the first nominating contests near.

The focus also reflects an eagerness among many Republicans to make criticism of the Obama administration’s handling of national security central to the campaign — particularly if the Democratic nominee is former secretary of state Hillary Clinton.

In his latest ad, called “Safe,” Rubio swipes at President Obama: “While ISIS is beheading people and burning them in cages, he says climate change is our greatest threat.”

Elizabeth Wilner, senior vice president for political advertising at the media-tracking firm Kantar Media/CMAG, said the types of spots now being aired by GOP candidates are more commonly seen at the end of a campaign.

“These are the sorts of ads you usually see in October, when viewers have become somewhat fatigued and immune, and you have to go that extra mile to clearly distinguish the choice between yourself and everyone else,” she said. “Scaring people is the fastest way to create an ad that resonates.”

A group of super PACs supporting GOP candidate Ted Cruz is airing an ad featuring a montage of Islamic State militants, refugees on the run and rolling tanks. (Mark Kauzlarich/Reuters)

The traditional introductory ad laying out a candidate’s credentials has not made an impact so far this cycle, GOP strategists said.

“The saccharine bio spot is a thing of the past right now,” media strategist Brad Todd said. “I think the voters are at a point where they don’t have a high level of trust or confidence in anybody in politics.”

Some are skeptical that anyone can out-Trump Trump. The proliferation of terrorism-themed ads with footage of shadowy figures could create a muddle in the minds of voters, said Fred Davis, a veteran Republican admaker working for a super PAC backing Ohio Gov. John Kasich.

“I think the residual effect of so many messages on the same topic is a giant zero,” Davis said. “People will hear so many similar messages, they will get confused. No one will have great results.”

[Jeb Bush’s super PAC burning through money with little to show for it]

The dominant focus on national security in the GOP race comes after the recent attacks in Paris and San Bernardino, Calif., left voters deeply unsettled. In a December Washington Post-ABC News national poll, 39 percent of Republican-leaning voters said the threat of terrorism was the most important issue in their vote, outpacing the economy (28 percent), immigration (7 percent), and tax policy and health care (both at 5 percent).

“If we don’t have security, we won’t have a country,” said Lee Guthrie, a 76-year-old retiree who turned out to see Cruz in Guthrie Center, Iowa, on Monday.

Earlier in the day, at a campaign stop at a bar in Carroll, Iowa, Cruz vowed that he would “defeat radical Islamic terrorists.”

“We will not weaken, we will not degrade, we will utterly and completely destroy ISIS,” he said, using an acronym for the Islamic State as people cheered “Yeah!” and one man rang a cowbell.

Meanwhile, Rubio delivered one of his most aggressive speeches to date Monday, trying to position himself as the staunchest national security hawk in the field.

“When you vote for me, you will know exactly what you’ll get,” Rubio said in Hooksett, N.H. “You’ll get a president who will destroy terrorists overseas by authorizing whatever tools our commanders need.”

But Trump has been the most bellicose, pledging at his rallies to bar Syrian refugees, temporarily ban all Muslims from entering the country and “bomb the s---” out of the Islamic State. His first TV ad, which hit the air this week, features an image of a U.S. battleship launching a cruise-missile strike and photos of the killers in the recent California terrorist attack.

“We don’t know who’s coming into our country,” he told a crowd of thousands in Lowell, Mass., on Monday night. “And we’ve got to find out and we’ve got to figure out, because something’s going wrong when you have what happened in Paris, when you have what happened in Los Angeles, when you have what happened in California — where you have all of these incidents — when you have people flying airplanes into the World Trade Center.”

[Donald Trump’s provocative first TV ad raises the temperature of GOP race]

His rhetoric is resonating. Asked which of the leading candidates they would trust most to handle the terrorist threat, 50 percent of Republicans named the real estate tycoon, far outpacing Bush at 14 percent, Cruz at 12 percent, and Carson and Rubio at 9 percent, the December poll found.

Not every Republican is playing along. Sen. Rand Paul (Ky.), whose non-interventionist views have marginalized him in the wake of the Paris attacks, said the fear-based appeals could backfire. “Polls go up and down depending on current events,” he said.

And some Democratic strategists are doubtful that fears of terrorism will ultimately determine the outcome in 2016.

“The degree of anxiety will probably rest on whether there are other events of a major nature that intrude on the race,” said former senior Obama adviser David Axelrod, adding: “I continue to believe that the economy is the most durable and important issue.”

But Todd, the media strategist, said national security is “the single best way to encapsulate the failures of the current administration — it’s the failure of their ideology and their competence,” and he said that Clinton “is the most vulnerable on the president’s policies in the Middle East.”

For her part, Clinton regularly denounces her GOP rivals for using fear as a campaign tactic. In Keene, N.H., on Monday, she told a questioner, “I think there’s a lot of anger, frustration, insecurity, fear in our country right now.”

But, she added: “I think it’s the responsibility, as somebody in leadership or vying for leadership, to understand that but not to inflame it. Not to use the kind of really abrasive and insulting rhetoric that we’ve heard too much of and to set people against one another.”

Scott Clement and Robert Costa in Washington; Anne Gearan in Davenport, Iowa; Jenna Johnson in Lowell, Mass.; Ed O’Keefe in Manchester, N.H.; Abby Phillip in Keene, N.H.; Sean Sullivan in Burlington, Iowa; David Weigel in Orange City, Iowa; and Katie Zezima in Guthrie Center, Iowa, contributed to this report.