At the Conservative Political Action Conference (CPAC) this week, you might have expected to see evidence of the debate raging in the Republican Party over its approach to foreign policy. Instead, the GOP's loudest and most aggressive foreign policy instincts were on most prominent display. It was less a soul-searching moment, and more hawkfest 2015.

At a marquee foreign policy panel, for example, Sen. Tom Cotton got the biggest applause for this line: "Hillary Clinton, John Kerry, and Joe Biden made the right decision to support George Bush in the Iraq war." About ten seconds later, Rep. Ryan Zinke (R-MT), who like Cotton is an Iraq vet, denounced the 2003 decision to invade. The crowd was silent.

That's as a good a summary of the CPAC approach to foreign policy as you can get. A hawk was cheered. A skeptic was ignored.

And while CPAC appeals to the most conservative wing of the party, the rise of the hawks here is part of a much broader trend in the GOP. There are three big reasons for the return of the GOP's aggressive foreign policy and each says something important about the 2016 race.

1) The ISIS crisis

Every plausible candidate for the 2016 GOP nomination - with the notable exception of non-interventionist Rand Paul - has advanced a pretty aggressive approach to world politics. The place it is most true: ISIS, which was clearly CPAC's most popular foreign affairs topic. At times, the conference felt like a competition as to who could be more aggressive with respect to the group.

"ISIS represents the worst threat to freedom since communism," former Texas Governor Rick Perry said.

"We kill the terrorist leaders before they kill us," Sen. Ted Cruz, also of Texas, said.

Governor Bobby Jindal (LA) won huge applause for demanding that America "hunt down and kill these radical Islamic terrorists."

There's a reason that ISIS, more than Iran or Russia, took the spotlight at CPAC. They are a simple, unambiguous evil — one that harkens back to the early 2000s, when the GOP's war on terrorism rhetoric helped it dominate Democrats at the polls before Iraq went sour.

Moreover, the group's June 2014 rampage across northern Iraq appears to have transformed the party base's feeling on foreign affairs. In November 2013, only 18 percent of Republicans told Pew the US was doing "too little" to "solve world problems." By August 2014, that figure jumped up to 46 percent, a plurality. In February 2015, 86 percent of Republicans said that ISIS was a major threat to the US in a CBS poll; 72 percent supported using US ground troops against it.

So it makes sense that, at a major conservative conference, Republican primary candidates would take aggressive, hardline positions on ISIS. The audience - the sort of people these prospective candidates need in a primary - wouldn't approve of anything else.

2) Barack Obama

It's not just ISIS that gives Republican 2016 candidates an incentive to tack hawkish: it's also President Obama himself.

Throughout his presidency, Obama has adopted a fairly restrained approach to world affairs. Given Republicans' toxic view of Obama, candidates have an incentive to run in the exact opposite direction.

And after the slew of global crises that plagued 2014, it looks like the general electorate is starting to share their view. A Pew poll released on February 26 found that, for the first time in Obama's presidency, the public believes Republicans could do a "better job" handling foreign policy than Democrats.

"Nobody is going to run in 2016 and say 'eight more years of Obama's defense and foreign policy,'" James Jay Carafano, the director of the Heritage Foundation's Institute for International Studies, said at CPAC's big foreign policy breakout session. He was, quite clearly, speaking for the Republican field.

3) The party infrastructure

The foreign policy panel was revealing in another way. Besides Carafano, Sen. Cotton, and Rep. Zinke, the last panelist was John Bolton, George W. Bush's famously hawkish Ambassador to the UN. Zinke's retrospective opposition to the 2003 Iraq war aside, all four of the panelists endorsed a fairly muscular approach to current international challenges.

After a discussion on Iran, for example, moderator KT McFarland summarized the panel's policy proposals as "regime change, regime change on steroids, and bankrupt the bums." That's basically accurate, and indicative of the state of the Republican party's foreign policy apparatus.

From the congressional level down to conservative think tankers and party activists, there just isn't a big institutional home for non-interventionists. CPAC's big-name foreign policy panel was stacked with hawks because the conservative movement is stacked with hawks. That means no Republican candidate is likely to buck the hawkish consensus unless they have really strong electoral or ideological reasons to do it.

Where does that leave Rand Paul?

Rand Paul is the major exception. Paul's libertarian approach to foreign policy sees an aggressive foreign policy as just another big government program, likely to fail in the same way that most government programs do. Needless to say, that put Paul at odds with the prevailing hawkish mood at CPAC.

Certainly, Paul has a devoted following. Walking around CPAC, you see Paul fans everywhere, decked out in "Stand with Rand" t-shirts (a slogan popularized by his famous talking filibuster in opposition to the Obama administration's targeted killing of American citizens suspected of terrorism abroad). This fandom gave Paul's speech at the main session, which bashed "Hillary's war in Libya," a rapturous reception.

But even Rand supporters know that foreign policy could be the issue that kills his candidacy. Foreign policy "is his Achilles heel," Jonathan Beale, a youthful guy sporting a Young Americans for Liberty pin, told me while waiting in line for Sen. Paul to sign a copy of his book.

"If ISIS scares [Americans] enough times, I don't think Rand has a chance," Paul Fosse, a county coordinator for the Campaign for Liberty, told me as he passed out Paul-friendly literature.

Judging from their speeches, the other Republicans clearly get this. They're willing to adapt to the prevailing mood inside the party on foreign policy while Paul's ideological commitments prevent him from doing so. It looks like CPAC will be the first of many conservative gatherings where, on foreign policy, Rand stands alone.