When we look back decades from now, one of the keys to understanding this period in our political history will be the story of how a set of market-based health insurance reforms that started as a proposal from the Heritage Foundation and then were successfully implemented by a Republican governor who later became the GOP presidential nominee, ended up being viewed by virtually all conservatives as not just an abomination but the very essence of statist oppression. Liberals have often expressed wonder or exasperation about the way conservatives changed their opinions about this particular brand of reform. But now that it's driving a government shutdown (and soon a potential default on the debt), we have to acknowledge that it's more than just a policy conservatives hate. The Affordable Care Act is far, far bigger than that. It has become the most important definer of conservatism in America circa 2013. It isn't that conservatives don't still want to cut taxes for the wealthy, or slash the social safety net, or liberate corporations from pesky regulations on worker safety and the environment, or make it impossible for women to get abortions, because they still want all those things. But Obamacare has swallowed conservatism whole.

Since the health-care exchanges opened yesterday, some have suggested that the increased attention brought to the fact of their opening by the shutdown has done the administration a favor, informing more people that open enrollment has begun than the Department of Health and Human Services could possibly have managed on its own. That's probably true. This controversy has also served to remind conservatives that there is nothing more important than fighting Obamacare. Every Republican politician has to prove that their hatred of the law is as great as that of the angriest Tea Partier. Every conservative everywhere is being told that this is what it means to be a conservative, this is so important to their beliefs and the future prospects of their party and their ideological movement that it is worth laying waste to the government and even the economy itself. If you're a conservative and you aren't willing to risk everything on even the smallest chance to toss your spear into this foul beast's heart, then you're not really a conservative at all.

Let's fast-forward a couple of years from now, after this crisis ends without the ACA being defunded or delayed. The law is all rolled out, and while it's far from perfect, things are going pretty well. We don't have universal coverage, but the vast majority of Americans now have insurance, including millions who didn't have it before. It's not dirt cheap, but the trends that are evident today-a slowdown in the overall health-care spending growth rate, mirrored by a slowdown in premium increases-are continuing. More states have put aside their ideological objections and accepted the expansion of Medicaid to cover all their poor citizens, even if there are a few straggler states left. What with "pre-existing conditions" and "job lock" things of the past, even the most doctrinaire Tea Partier admits that there's no more question about whether Obamacare can be repealed. Its tendrils have reached too many people who now benefit from it and would react angrily if you tried to take it away.

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Ted Cruz admitted to Sean Hannity back in July that "If we don't [defund Obamacare] now, in all likelihood, Obamacare will never, ever be repealed. Why is that? Because on January 1, the exchanges kick in, the subsidies kick in," and they'll be unable to take away something people are benefiting from. And he's surely not the only Republican who gets this, which is part of the explanation for the ferocity with which they're fighting now. But in our future scenario, the fight over the law will be basically over. There might be some debates about adjusting parts of the law, as Democrats will want to do, but that won't concern Republicans too much. Once there's no possibility left that it can be killed, they'll likely lose interest.

I think that's the most plausible picture of what things will be like in, say, 2015. The question is, if eventually they have no choice but to accept that the argument over the ACA is settled, what on earth will Republicans do with themselves? Because over the last four years, opposition to Obamacare has taken on such an extraordinary power within the movement that all other issues have paled before it.

Sure, they could revert to the old standbys-Cut taxes! Cut regulations! Strong defense! But those are just positions you can take. Obamacare was a war to be fought. And nothing galvanizes, energizes, and defines us like our wars. That's particularly true of the zealots who are driving the Republican party and form such a key part of its base. And if they aren't fighting Obamacare, who will they be?