The entirely plausible outcome of the Supreme Court’s decision on the Affordable Care Act that has received the least attention is what might be called a “split decision:” an invalidation of the individual mandate alone, with the rest of the law left to stand. This possibility has been shirked in part because it’s easier to do so, and in part because the Obama administration did not defend “severability” in the famous oral arguments before the Court in March (though an “independent” attorney did). But as TNR’s Jonathan Cohn notes today, the latest hot rumor is that this is in fact the issue the Court is still agonizing over (there’s also been a rumor, he says, that one Justice became so wrought up over the deliberations that he or she took his or her clerks out for a drinking binge).

Cohn goes on to argue passionately that ACA would still do an enormous amount of good even without the mandate, which is usually considered essential to the task of building a broad enough risk pool to make the expansion of coverage feasible (i.e., to avoid big and politically disastrous jumps in premiums). But he admits no one really knows exactly how it would all play out.

But regardless of the long-term effects, a split decision would create some really interesting political challenges to Republicans. Without the mandate as a straw man, GOP demands to repeal the entire law would have to focus more squarely on the more popular aspects of ObamaCare, most notably the guaranteed-issue and community-rating provisions. Republicans have campaigned avidly on the “Medicare cuts” in the law, but without the complex dynamics introduced by the mandate, continuing that talking point would more obviously align them with a budget-busting demand to restore a Medicare Advantage program whose main fans are insurance companies. And while they might go after the subsidies designed to make the new, expanded coverage affordable–which would be even more important to the law’s design if the mandate is gone–as “welfare,” an awful lot of middle-class folk would be eligible for the subsidies. More subtly, the complexity of ACA, which has worked to the political advantage of its critics, might begin to work against them if they are forced to justify more specific objections.

Above all, for all the talk on Capitol Hill of Republicans getting themselves prepared for the questions they will face if ObamaCare is overturned, I doubt they’ve been successful in game-planning a split decision. Without the unifying emotionalism associated with the mandate, maintaining unity between pols-reading-polls and conservative activists who think any kind of action to deal with the uninsured is socialistic won’t be easy.

In any event, it shouldn’t just be Democrats who are nervous about the possibility of a 5-4 decision that strikes down the mandate but leaves the rest of the law intact. Things will get crazy very fast.

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Ed Kilgore is a political columnist for New York and managing editor at the Democratic Strategist website. He was a contributing writer at the Washington Monthly from January 2012 until November 2015, and was the principal contributor to the Political Animal blog.