As recently as two years ago, it appeared that the 2016 presidential contest was likely to become a monumental debate within the Republican Party over national security and foreign policy.

But not anymore. Although national security is Topic A for the growing field of candidates for the GOP nomination, it is becoming harder to discern any differences among them.

The contenders are a hawkish group — at least in their sound bites. Sen. Rand Paul (R-Ky.) has been the most skeptical of military intervention and government surveillance, but even he has proposed increasing defense spending and staged an event during his announcement tour in front of an aircraft carrier in South Carolina.

Beyond criticizing President Obama — whose handling of foreign policy is getting low marks in opinion polls — the Republican candidates have offered few specifics of what they would do differently.

“At this point, it’s mainly about the adjectives,” said Daniel W. Drezner, professor of international politics at Tufts University’s Fletcher School of Law and Diplomacy. “In terms of how they are distinguishing themselves from each other, I can’t tell you.”

Added Jon B. Alterman, director of the Middle East program at the Center for Strategic and International Studies: “What they’re saying is they would get different outcomes, but nobody is really asking them how.”

That is in part because, however disappointed Americans are with the results of Obama’s foreign policy choices, they have little appetite for alternatives, such as committing U.S. ground troops to trouble spots in the Middle East. Voters also remain largely supportive of other Obama initiatives, including negotiating directly with Iran regarding its nuclear program.

Although their talk is tough, the GOP contenders’ foreign policy résumés are thin.

Marco Rubio (R-Fla.), a 43-year-old freshman senator, boasts that he has the deepest experience of any of the leading contenders by virtue of having served on both the Senate foreign relations and intelligence committees for the past four years. He is set to give a policy speech on Wednesday before the Council on Foreign Relations in New York.

“Few, if any, have spent the amount of time on it that I have,” Rubio told the Des Moines Register in February.

Wisconsin Gov. Scott Walker is making his first trip to Israel this week.

“We need a commander in chief who will once and for all call it what it is, and that is that radical Islamic terrorism is a threat to us all,” Walker said to applause at a gathering of Republican activists in South Carolina on Saturday. “We need a president who will affirm that Israel is our ally, and start acting like it.”

But Walker also conceded that foreign affairs is not something he has dealt with on a day-to-day basis as a governor. “It has increasingly become one of the most important things for me to focus on,” he said.

The Democrats, meanwhile, appear all but certain to put forward a former secretary of state, Hillary Rodham Clinton, as their nominee.

Republicans note that Obama himself was a freshman senator when he was elected in 2008.

Historically, GOP candidates have received more trust from voters when it comes to international affairs. Over the past half-century, the Republican Party has produced nominees with compelling credentials in that area — including Dwight D. Eisenhower, Richard M. Nixon, George H.W. Bush, Robert J. Dole and John McCain.

And although Ronald Reagan may have lacked international experience, the former California governor was strong and clear about his philosophy as a cold warrior who would build up the military.

Looming over the GOP, however, is the more recent foreign policy record of George W. Bush. Polls consistently show that a vast majority of Americans now think the Iraq war was not worth the cost of nearly 4,500 American lives.

Bush’s brother Jeb Bush, a ikely GOP presidential candidate who has struggled to both distance himself from and embrace his family, told Fox News Channel’s Megyn Kelly that he, too, would have authorized the invasion, which was based on incorrect intelligence about Iraq’s weapons capability.

On Monday, he had to do a second interview on the radio program of conservative host Sean Hannity to attempt to clarify that comment.

“I interpreted the question wrong, I guess. I was talking about, ‘Given what people knew then, would you have done it?’ ” Bush told Hannity. “Knowing what we know now, clearly there were mistakes as it related to faulty intelligence in the lead-up to the war and the lack of focus on security. My brother’s admitted this and we have to learn from that.”

Given a do-over on the question of what he would have done, Bush said: “I don’t know what that decision would have been. That’s a hypothetical, but mistakes were made, as they always are in life.”

The main reason international affairs are at the forefront of campaign rhetoric is that they cause voters great anxiety. Even as the economy at home improves, the world is looking like a scarier place, particularly since the rise of the Islamic State group, which has publicized the beheadings of its hostages.

The Pew Research Center’s most recent annual survey of Americans’ policy priorities found that, for the first time in five years, the percentage who cited defending the United States against terrorism as a top issue (76 percent) was as high as it was for those who said the same about strengthening the nation’s economy (75 percent).

The focus is particularly intense among Republicans. In an April poll by the Wall Street Journal and NBC News, 27 percent of GOP voters cited dealing with national security and terrorism as their biggest priority for the federal government — up 19 percentage points from 2012 and the highest of any issue.

By comparison, only 13 percent of Democrats said it was their leading concern — ranking behind job creation and economic growth, health care and climate change.

Other factors in the positioning of the GOP presidential field are the new realities of campaign finance, and the importance of Israel in particular to mega-donors such as Las Vegas casino magnate Sheldon Adelson.

The Republican Jewish Coalition says it has drawn scores of new contributors as a result of the tensions between Obama and Israeli Prime Minister Benjamin Netanyahu over how to curb Iran’s nuclear capabilities.

Then again, it is a well-trod strategy for candidates whose party is out of power to accuse whoever is in the White House of alienating the nation’s allies and neglecting threats. Obama did it in 2008.

Fault lines remain in the Republican Party on the question of the United States’ role in the world, and on how far the government should go at home to monitor its citizens. And there will be flash points in the months ahead in presidential debates and in congressional votes on national security questions.

In March 2013, Paul created a sensation by talking for nearly 13 hours straight in the Senate chamber against the Obama administration’s use of unmanned drones.

Rubio and Sen. Ted Cruz (Tex.) — now Paul’s rivals for the GOP nomination — joined him in that unsuccessful effort to block the nomination of John Brennan as Central Intelligence Agency director. Paul and Cruz were labeled “wacko birds” by their fellow senator McCain (Ariz.), who was the 2008 Republican presidential nominee.

More recently, Paul and Cruz applauded a federal appeals court ruling that the National Security Agency’s collection of million of Americans’ phone records violates the law. Rubio defended the government’s data-collection program, and Jeb Bush has also expressed support for it.

Paul is also planning to filibuster the reauthorization of the USA Patriot Act, the 2001 law that provides the underpinning for the surveillance program.

“We will be trying to stop it. We are not going to let them run over us, he told the New Hampshire Union Leader on Monday. “And we are going to demand amendments and we are going to make sure the American people know that some of us at least are opposed to unlawful searches.”