The political battle over the Iran deal is going to be the biggest foreign policy fight of Obama's presidency. Congress has the power to destroy the deal, and Republicans will do their damnedest to try to use it, however unlikely it is that they'll succeed.

But this is more than just a policy dispute, and that's why the fighting is taking place in more than just Congress. Cable news is spinning itself into a froth over whether the Iran deal is a horrifying catastrophe or a golden day in global progress. Odds are good that you've already gotten sucked into, or at least worked to avoid, an argument on Facebook over this.

People have strong feelings about this deal — very strong feelings. Maybe that's partly because they are just that emotionally invested in the details of arms control agreements, or in the triangulations of American Middle East policy. Or maybe there's something more going on here.

The argument is so fierce because it's actually an argument about something much bigger, for Americans, than a nuclear deal with Iran. It is larger even than people's feelings about Obama. It is, rather, the culmination of an argument that America has been having with itself for years about the kind of country it wants to be in its relationship with the rest of the world.

The Iran deal is driving this debate for several ones, but the most important is that it represents the clearest, brightest point of disagreement between the two dominant ways we think about foreign policy in the US. It perfectly captures the divisions between the center-left worldview and the more hawkish neoconservatism that dominates the right. It's everything that liberals like Obama want foreign policy to be — and everything neocons hate.

And if Obama manages to keep the deal in place, it will be a major, and potentially very long-term, policy defeat for American hawks.

The Iran deal is a liberal dream

The best way to understand Obama's foreign policy is as a reaction to George W. Bush. Obama won the Democratic primary on the back of anti–Iraq War sentiment. His promise was to never repeat that kind of disastrous mistake again.

Obama wasn't alone. During the Bush years, a strain of thinking on the center left emphasized the need to avoid foreign policy blunders and respect the limits of American powers. Often called "progressive realism," it called on the United States to pursue a limited set of interests and goals, and do so through nonmilitary, ideally multilateral means. The US can solve some foreign problems, but not all of them; Diplomacy, even with dictators, is almost always more effective than war.

In the Middle East, that meant abandoning the Bush administration's attempt to rid the region of tyranny and supplant it with democracy. It meant identifying specific threats to American interests and regional stability and trying to solve them without embroiling the United States in another regional war.

At the same time, this process of center-left foreign policy rethinking was happening on a much broader and more basic level than just think tank meeting rooms and campaign policy planning sessions. There is a reason Obama's anti-war agenda was so popular in 2008, and that two years earlier voters had swung en masse to Democrats.

This was a popular movement that was outraged at Bush-style foreign policy and badly wanted a new way forward in the world. It was, and still is, something that a lot of left-leaning Americans care about deeply, as an issue of what kind of role in the world they want to play.

Nothing better encapsulates this way of thinking than a nuclear deal with Iran. The deal addresses one major regional problem — Iran's nuclear program — without attempting to solve all of the region's crises. It forecloses the possibility of a disastrous American war with Iran, at least in the foreseeable future, and opens up a channel for greater diplomatic cooperation with Iran on other problems down the line.

The deal is, in many ways, the exact opposite of the 2003 US-led invasion of Iraq. That was a largely unilateral and highly idealistic effort to reshape the Middle East by imposing American force. In Iran, it is international inspectors and diplomats, not American service members, who will be seeing this through. The deal is about accommodating international will and turning it toward American interests, rather than defying it.

The deal's design is so effective, if you believe arms control experts, that Iran's path to a bomb will likely be blocked for at least a decade. Diplomacy worked. And it worked better than America acting alone. For Obama and like-minded liberals, that's a perfect example of how foreign policy should be done.

It's also a neoconservative nightmare

The overwhelming majority of right-leaning defense intellectuals and Republican politicians belong to the neoconservative school of thought, in which this deal looks very different. For them, the Iran deal isn't a vindication of diplomacy. It's abject surrender of everything America should stand for.

Because neoconservatives believe in America's extraordinary power to shape the world, they believe the US should have been able to force Iran to give up its entire nuclear program — as well as every other policy we don't like.

The deal "means recognizing that the United States cannot bludgeon Iran into total submission, either economically or militarily," Peter Beinart writes at the Atlantic. "It is precisely this recognition that makes the Iran deal so infuriating to Obama’s critics."

But it's more than just that: The fact that this is Iran makes it all the more painful for hawks. Iran has built much of its foreign policy identity around defying America and American power, from the 1979 hostage crisis to its activities in the Iraq War. For Obama to negotiate and compromise with the Iranians, then, feels to hawks like a dangerous admission not just that American power has limits, but that defying America works (especially if, as hawks believe, Iran will exploit the deal to get a bomb anyway).

As with the center-left foreign policy that Obama represents, this hawkish view of the world is popular with many Americans, not necessarily all Republicans and certainly beyond the members of neoconservative intelligentsia. It feels good to think of yourself as belonging to a country that is not just a bright shining beacon on the hill, but is indeed the guardian of all that is right and good in the world.

There's a reason hawks so often refer back to World War II, and see the world through this lens. It's a way of seeing an America that is morally righteous as well as strong. That's something that people want to be a part of. Compromising on that vision, then, feels like compromising on those values — and thus, seeing your country move away from what you think it is. That's painful, and it's scary. It is little wonder people would reject and resist it.

The stakes

By the time a Republican could feasibly take over the White House, the deal will almost certainly be irreversible. Sanctions relief will likely begin in 2016. By 2017, the United States will be locked in; it will be unable to back out of the deal unilaterally and revert back to the pre-deal status quo, without being blamed for the deal's collapse and losing the sanctions coalition.

Obama's deal, then, isn't a temporary setback for neoconservatives: It is a very long-term, and potentially even permanent, policy defeat.

Which is why the fight in Congress is going to be so very, very bitter. The Iran oversight bill, called Corker-Cardin, gives Congress a bit of time to block sanctions relief while it reviews the Iran deal. Unless it actively chooses to block the deal, and has enough votes to overcome Obama's veto, implementation will begin apace.

So neoconservatives have one last chance to stop what they see as an ultimate disaster for American foreign policy. Obama, by contrast, will be working to save what he sees as the ultimate vindication of his approach to foreign policy.

That will be a bitter fight in Congress for sure. But it will also be a vehicle by which Americans rehearse, often painfully, this larger argument about the kind of country they want to have. It'll be a fight over Iran policy, but like so many big political debates, it is really about us.