WASHINGTON » Gruesome killings by the Islamic State, terrorist attacks in Europe and tensions with President Vladimir Putin of Russia are reshaping the early Republican presidential race, creating anxiety among party voters and sending potential candidates scrambling to outmuscle one another on foreign policy.

Doubts that crept into the minds of conservatives about engagement abroad after George W. Bush’s presidency and the protracted war in Iraq are dissipating, and members of the Republican party are increasingly pressing for more action against the Islamic State.

Nearly three-quarters of Republicans now favor sending ground troops into combat against the Islamic State, according to a CBS News poll last week. And in Iowa and South Carolina, two early-nominating states, Republicans said military action against the group was, alongside economic matters, the most important issue in the 2016 election, according to an NBC survey released last week.

"There’s a lot of fear out there," said Katon Dawson, a former chairman of the South Carolina Republican Party, noting that the Islamic State, also known as ISIL, had become a regular topic of discussion at his regular breakfast spot in Columbia, the Lizard’s Thicket. "The waitresses and managers and everybody there has a notion about ISIL. People understand who this group is now."

The emphasis on foreign policy is also a tacit acknowledgment by Republicans that, with the economy improving, they need another issue to distinguish themselves from Democrats. And it offers them a way to link former Secretary of State Hillary Rodham Clinton to President Barack Obama on an issue where the president’s approval ratings are weakening.

More immediately, the hawkishness now defining the early campaign could imperil the presidential hopes of Sen. Rand Paul of Kentucky, the libertarian-leaning Republican who embraces a more restrained approach to U.S. engagement with the world.

"The guy who’s now got the biggest challenge because of this is Rand Paul," said Newt Gingrich, the former Republican House speaker. "The Rand Paul worldview, which I suspect will change, is just incompatible with reality."

Although Paul will not formally announce his campaign until April, prominent Republican officials and groups are already organizing to undercut his approach. One of the party’s biggest donors, the Las Vegas casino magnate Sheldon Adelson, has told associates he is open to underwriting an effort to stopping Paul, should he gain traction in the primaries.

At least two Republicans, John R. Bolton, the former U.N. ambassador, and Sen. Lindsey Graham of South Carolina, are considering their own White House bids largely to draw attention to the need for a more muscular foreign policy.

One international affairs expert who has advised Paul and hails from a similar, more restrained school of foreign policy said the revival of terrorism as an issue would force the senator to explain his views more thoroughly.

"He’s got, to some extent, to be an educator in this process," said the expert, Richard R. Burt, a former ambassador and State Department official under President Ronald Reagan. "He needs to talk through with primary voters the kinds of questions that need to be asked before we commit U.S. forces abroad: How we can’t just have a visceral reaction. How does this impact American interests and security?"

But Paul’s detractors are not going to make that easy.

"I think most of the Republican candidates or prospective candidates are headed in the right direction; there’s one who’s headed in the wrong direction," said Bolton, suggesting most Republicans would be "horrified" by Paul’s views on international affairs.

Bolton has formed three separate political groups to promote pro-interventionist Republican candidates. His newest effort, called the Foundation for American Security and Freedom, will be a 501(c)(4) tax-exempt group, meaning that it can accept donations from contributors who wish to remain anonymous.

Graham has formed a similar group, Security Through Strength, and has begun traveling to early-nominating states to discuss what he calls "the threat of radical Islam" as he ponders a presidential run.

Mike Rogers, the former Michigan representative and the former chairman of the House Intelligence Committee, is not considering a presidential bid, but he is trying to influence the 2016 race by creating an organization called Americans for Peace Prosperity and Security, which he said would support candidates "who understand the importance of American engagement." His group is scheduled to host its first forum in Iowa in May and is considering holding a large candidates’ forum in the fall.

The combined efforts of these groups, along with the shift of rank-and-file Republicans toward hawkishness, could isolate Paul. This is will be most vividly apparent once debates begin this year. With Republican candidates increasingly attacking Obama for what they see as his unwillingness to project U.S. strength, Paul’s support for the administration’s policies on such issues as negotiations with Iran over its nuclear program will stand out — and force him into some awkward situations.

"You’re not going to find any of the Republicans, even those who might well have behaved like Obama, standing up and defending Obama," said Richard Perle, a pro-interventionist defense official who served in the Reagan administration.

The movement of Republican public opinion is striking. In 2009, worn down by the long and unpopular Iraq War undertaken by Bush, about 53 percent of Republicans said that the United States should "mind its own business" internationally and let other countries get along the best they can on their own, according to a Pew Research Center survey.

But the shocking images of terrorism and Obama’s approach to them have set off much concern among Republican voters, said Sen. Kelly Ayotte, R-N.H. Ayotte recalled that, after she spoke at a recent party dinner in her home state, Republican activists had approached her to discuss the threat of the Islamic State and the Obama administration’s nuclear negotiations with Iran.

"National security issues have really risen to the top in the presidential race, and that’s because of what we’ve seen happening around the world and in part because of the ineffective policies of this administration," Ayotte said.

Even last week, as former Gov. Jeb Bush of Florida sought to distance himself from his brother’s foreign policy record at a speech in Chicago, he found himself embracing the sort of muscular engagement that had characterized the 43rd president’s administration.

The former Florida governor called nonstate terrorists groups such as the Islamic State "perhaps the greatest security threat that we now face for our own homeland."

He added, "Taking them out is the strategy."

Paul and his backers have been conflicted about how to respond to the shift, and to the senator’s hawkish critics.

They have courted them at times; Paul has aggressively sought out Republican Jewish Coalition donors and dropped by one of their events at a Washington steakhouse this year that Adelson attended. His team has even sought to flatter the neoconservative Washington Free Beacon, offering the site exclusives about Paul’s bill to eliminate U.S. aid to the Palestinians (which the Free Beacon noted promptly came hours before he was to meet with Jewish donors).

But when challenged, Paul can also strike a pugilistic note. Referring to Bolton and other critics, Doug Stafford, Paul’s top political adviser, accused them of trying to promote their own political brand at Paul’s expense.

"Can you run for secretary of state?" Stafford asked. "They are going to lie about who Rand is and what he stands for. That’s what they do. We will be ready for them."

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