The divisions within the Republican Party, important and often intense as they are, tend to be more about tactics than substance. Militant tea party Republicans and the supposedly moderate establishment Republicans both want to destroy the Affordable Care Act, for instance, but the former believe shutting down the government is a good way to accomplish that goal, while the latter disagree.

But we may be seeing the emergence of a genuine, substantive split within the GOP on foreign policy, with a significant faction not only rejecting the most important Republican foreign policy initiative of the last couple of decades (the Iraq War), but formulating ideas that could produce different kinds of decisions in the future.

You may be thinking, “Oh, you’re talking about Rand Paul,” and I am, but it’s not just him. While Paul is eager to tell anyone who’s listening that he’s no isolationist, this week he committed a rather dramatic heresy by saying explicitly that invading Iraq in 2003 was a mistake. “All the way back to the Iraq War, I think it was a mistake to topple Hussein. Hussein was the bulwark against Iran,” Paul said. “I’m worried [Iran] is twice as strong as it was before the Iraq War.”

This is significant for a couple of reasons. First, support for the Iraq War defined Republican foreign policy for a decade, and for someone running a serious candidacy for president to turn his back on it while still trying to win his party’s presidential nomination is remarkable. Second, Paul’s justification involves an acknowledgment that military action can have serious, even catastrophic unintended consequences, something Republicans haven’t been too eager to talk about in recent years. They’re much more likely to present military action as simple and straightforward.

While there are plenty of Republicans who will disagree, Paul is not alone. As conservative columnist Matt Lewis wrote: “What Paul said about Iraq takes guts. There are surely plenty of Republicans across the country who privately agree with him. But there are many more — and not just Bush-era neocons — who will never cop to this publicly.”

Last night, the Daily Caller published an interview with Ted Cruz in which he lays out the “Cruz Doctrine.” Its first two points are the same thing everyone always says about foreign interventions — that they should have a clear objective and be undertaken with overwhelming force. It’s the third point that differs:

“Third, we should get the heck out,” he said. “It is not the job of the U.S. military to engage in nation building to turn foreign countries into democratic utopias.”

Cruz’s foreign policy differs from Rand Paul’s because, among other things, he appears more willing to commit American military might if necessary than the Kentucky senator, such as potentially in Iran. But Cruz sometimes opposes more hawkish senators like John McCain, Lindsey Graham and — arguably — Marco Rubio because he doesn’t believe America should use the military to help spread democracy abroad.

While the interview didn’t mention George W. Bush, this is a clear rejection of the grandiosity of Bush’s foreign policy, in which we send our military to a foreign country, depose a dictatorial government, and then stay for years to build a democracy. Perhaps Cruz has taken the experience of the flourishing and peaceful nations of Iraq and Afghanistan to heart.

We should be careful not to overstate the diversity of thought within the GOP. Most Republicans will still say that invading Iraq was a splendid idea (even if it ran into a few bumps along the way and Barack Obama ruined the whole thing), and the idea that democracy-building is a fool’s errand is far from a majority position within the party. And Cruz and Paul, like other Republicans, still favor a good bombing campaign here and there. But I suspect that it isn’t just Iraq that’s causing this kind of rethinking — it’s Syria and Iran too.

While people have taken a variety of positions on Syria, even those most eager for us to intervene will admit that the situation is enormously complex. Even the barest understanding of the civil war makes clear that deposing Bashar al-Assad, brutal dictator and war criminal though he may be, could well lead to chaos and the installation of an Islamist regime no less oppressive. Even the most hawkish Republican wouldn’t be so stupid as to suggest that the application of military force could result in a flowering of Syrian democracy.

And on Iran, those who want to reject any possibility of a nuclear deal and start planning the bombing campaign will hurry to emphasize that they don’t want to invade. The military intervention they’d like would be limited to targeting the country’s nuclear facilities — a finite, if important, goal. Whatever they may actually think, they aren’t going to invoke the image of American soldiers patrolling the streets of Tehran.

In short, when it comes to the places the next Republican president will be under pressure to invade, things look extremely complicated, with another disaster a real possibility. Some of the candidates are as hawkish as ever, and there’s one who isn’t going to step away from the Bush Doctrine, since his name just happens to be Bush. But in the presidential primaries we could see a real foreign policy debate, not just over which candidate can condemn Barack Obama with the most vehemence, but over what the next Republican president should actually do.