A world on fire has reoriented the fight for the Republican presidential nomination, with candidates engaged in an elemental struggle to prove their strength as potential commanders in chief as national security moves to the top of many voters' list of concerns.

The debate shifted quickly after Nov. 13 terrorist attacks in Paris - the bloodiest since World War II - for which Islamic State claimed responsibility.

Reminders that it's a dangerous world followed in quick succession: Brussels was locked down; jihadists attacked a hotel in Mali; and Turkey shot down a Russian military jet involved in operations in Syria, perhaps the sharpest conflict with NATO since the end of the Cold War.

"Until this happened, national security was not in the forefront for most people," said South Carolina State Rep. Gary E. Clary, cochairman of Ohio Gov. John Kasich's campaign there. "You'd hear about education, big government, you name it. Paris really focused the campaign. . . . There are certain benchmark days in life, and this was one."

Polls captured the change, and candidates ratcheted up their rhetoric.

In New Hampshire, 42 percent of likely Republican primary voters said that terrorism and national security was the most important issue facing the nation. By comparison, 18 percent picked jobs and the economy - the usual No. 1 in modern campaigns.

Eight percent of respondents in a national daily tracking poll by Reuters/Ipsos on Nov. 7 named terrorism as the most important problem, with 21 percent saying the economy was the biggest issue. By Nov. 24, 27 percent named terrorism as their chief concern, compared with 15 percent who identified the economy.

"This is a war against humanity," Kasich said at a recent campaign stop at the Beacon Drive-In in Spartanburg, S.C. A few days later, Kasich vowed to "wipe ISIS off the face of the earth" in an appearance at the Hollis Pharmacy & General Store in Hollis, N.H., where campaign signs read, "A strong America is a safe America."

On Friday, Kasich's campaign launched its first television ad, called "Defending Our Way of Life," scheduled to air in Iowa, New Hampshire, and South Carolina.

"I've been arguing that America needs to assemble a coalition of our friends in Europe and our friends in the Middle East to destroy ISIS," Kasich says in the ad. "We destroy them in the name of humanity."

Former Florida Gov. Jeb Bush had focused his campaign on economic mobility, education, and fiscal responsibility - and often proclaimed he was "his own man" as he avoided talking about his brother's 2003 invasion of Iraq and his father's 1991 Gulf War.

After Paris, Jeb Bush embraced the family's interventionist Middle East legacy, calling Nov. 18 for a coalition of "overwhelming force," including U.S. ground troops, to attack ISIS in territory it holds in Iraq and Syria.

"If we don't protect each other, no one else will," Gov. Christie told an audience at the Park Place Lanes bowling alley in Windham, N.H., where he called for improved intelligence capability and a "broad coalition" to fight ISIS.

Throughout his campaign, Christie has sought to portray himself as the candidate best prepared to take on terrorists, citing his experience as a post-Sept. 11 U.S. attorney.

He is trying to make the case that his experience is even more relevant now. In a speech to the Council on Foreign Relations in Washington on Tuesday, Christie noted past showdowns with Sen. Rand Paul (R., Ky.) over the National Security Agency's telephone data surveillance program, which Paul opposes on privacy grounds but which Christie argues is needed.

"Eleven days after Paris, it's significantly more acute," Christie said of his argument.

Another by-product of the Paris attacks has been resistance among GOP candidates - and more than half the nation's governors - to President Obama's plan to resettle up to 10,000 more Syrian refugees in the United States. They warn that ISIS terrorists could slip into the country.

Ben Carson, who has led in Iowa but whose numbers are falling, went so far as to compare refugees to "rabid dogs."

A Quinnipiac poll out Tuesday shows that likely Iowa GOP caucus-goers oppose resettling Syrian refugees in the United States by an 81 to 15 percent margin.

Voters and operatives backing establishment-oriented Republicans expressed hope the new focus of the race would diminish the lead of front-runner Donald Trump, whose plan for ISIS is to "bomb the s- out of them."

So far, polling has shown Trump holding steady, with many GOP voters saying he is just the type of strong personality needed.

"He's strong and won't get pushed around," said Shane Arms, 46, of Taylors, S.C., who attended a recent Trump town hall in the state.

Republicans supporting the traditional candidates are hoping proven experience will matter with voters.

World events have "refocused primary voters into what's really important," said Joel Maiola, a New Hampshire Republican who served as chief of staff to former U.S. Sen. Judd Gregg, and who recently endorsed Christie. "They know that Donald Trump is somebody that's interesting to watch; he's like a slow-motion train wreck."

As New Hampshire's late-deciding voters "become serious," Maiola said, they will "understand the importance of having a steady hand that has depth."

The recent focus on terrorism "favors those who have something to say that sounds like a reasonable plan," said Fred Bramante, 69, an education consultant from Durham, N.H., who is leaning toward Florida Sen. Marco Rubio, Kasich, or Christie, "because I don't think they're crazy."

Ron Pockette, 58, a Navy veteran from Wellford, S.C., agrees that a steady hand is called for. He said he was considering Kasich or Rubio. As for ISIS, the rules of engagement that tie the U.S. military's hands need to be loosened, he said.

"We have to hunt them all down," he said. "Everything is too touchy-feely. We need to get it done and get out."

From the beginning of the Republican race, national security has had a more prominent role than in most campaigns. Of the recent Paris attacks, "that's just a blip," said Don McCoy, a Republican from Hollis, N.H., who attended the recent Kasich event there.

McCoy, who is considering a number of candidates, including Kasich and Rubio, said the attacks won't change his calculus: trying to decide who is the best leader. The rest will take care of itself.

"With the right leadership, these are problems we can solve," he said. "It's who's going to step forward to galvanize the country and move us forward."

215-854-2718@tomfitzgerald

INSIDE

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Parties far apart on climate and energy. A4.

In Fla., Trump ribs Rubio and Bush. A16.

Carson visits Jordan refugee camp. A17.

Racial selectivity seen in GOP drug views. A17.

Domestic surveillance

at issue. A18.

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