The state of Kansas recently asked to join the lawsuit challenging the constitutionality of the Obama health care plan filed by 20 state governments and the National Federation of Independent Business. Ohio, Wisconsin, and Wyoming are also seeking to join the multistate lawsuit, while Virginia and Oklahoma have filed separate challenges to the law. That brings the total number of state governments litigating against the plan to twenty-six. We now have a historically unprecedented situation where a majority of state governments are challenging the constitutionality of a major recently passed federal law. In our two hundred year history of constitutional litigation, that has never happened before.

Legally speaking, it doesn’t matter whether the number of states challenging the law is twenty-six or two. Indeed, it should not even matter whether any states oppose the law at all, so long as there is at least one private plaintiff with standing (and there are in fact many such). The arguments for and against the law will be the same.

But in politically sensitive cases such as this one, legal arguments are not the only factors that matter. The Supreme Court is usually reluctant to strike down a major federal law that has strong support from the president and his party and is a big part of their political agenda. In this case, however, the law in question is unpopular with the general public (see also here and here). And the states’ action is an indication that it is also disliked by a large part of the political elite. Widespread popular and elite opposition gives the Court the political cover that it would need to strike down the law. If the political winds continue to blow against the law, the justices can be confident that a decision to strike it down won’t create a dangerous backlash against the Court.

To be clear, I do not believe that the Court will strike down the law merely because it is unpopular or because the majority of state governments now oppose it. But the law’s unpopularity does ensure that the justices probably won’t hesitate to invalidate it for fear of a political backlash, if they are already inclined to do so for other reasons.