A federal district judge in Virginia has become the first to rule that one key provision of the Affordable Care Act is unconstitutional. I haven't read the decision carefully. But it appears that the judge believes that the federal government cannot require that all Americans have health insurance.

The government has argued that the constitution grants such authority via the power to tax and the power to regulate interstate commerce--an argument with which I, and quite a few legal experts, happen to agree. The judge, Henry E. Hudson, apparently sees things differently.

Hudson's decision was not a slam-dunk for repeal. He explicitly rejected arguments that the Affordable Care Act could not stand without the individual mandate. Of course, how well (if at all) the law could actually work without the mandate is a separate question. 

Hudson's ruling is not unexpected. He is a Republican appointee with a history of conservative rulings. Nor is it definitive. Two other federal district judges, Democratic appointees both, have already ruled that the entire law passes constitutional muster. A fourth decision, by a judge in Florida, is expected by year's end.

Most legal experts expect that, eventually, the case will come before the U.S. Supreme Court. Hudson himself acknowledged as much, writing “The final word will undoubtedly reside with a higher court."

And how might the five Republican appointees and four Democratic appointees on the Surpeme Court rule? Most court observers I know believe that at least one of the Republican appointees, most likely Anthony Kennedy, would agree with the government that the Affordable Care Act falls well within traditional boundaries of the taxing and interstate commerce powers. (For an example of such logic, see the Michigan ruling from a few weeks ago.)

I tend to think those experts are right, for reasons I'll get around to explaining one of these days. Then again, I recall hearing similar confidence about another highly anticipated court ruling--one about, oh, ten years ago.

For more on the mandate and some varied opinions on how an adverse ruling by the Supreme Court might affect the Affordable Care Act overall, see Aaron Caroll, Jonathan GruberEzra Klein, and Igor Volsky

Meantime, if you're looking for a more generic primer on the individual mandate, I highly recommend this video from the Kaiser Family Foundation.

(Updated at 2:15 p.m.)