It's in the constitution . . .

A majority of political activists, but libertarians especially, have the habit of labeling any law they think is really bad as "unconstitutional". I tried to avoid that sort of thing with the DC police cordon, because that's not really the point: lots of morally outrageous things are legal, and some laws are moral outrages.

But Orin Kerr at Volokh argues that in fact, the law isn't constitutional under current reading:

The Post story suggests that DC is relying on the Maxwell case as authority for legality of the checkpoint. And if the law were today what it was in 1996, I would say their legal case is certainly plausible.

The difficulty is that four years after Maxwell, the Supreme Court took a different turn in its cases in City of Indianapolis v. Edmond, 531 U.S. 32 (2000). In Edmond, the City of Indianapolis set up vecicle checkpoints to search for drugs. The city was worried that people were bringing narcotics into the city, and they figured that they could set up reasonable checkpoints to deal with the drug problem much like the earlier checkpoints had dealt with the problems of drunk driving and immigration. The Supreme Court disagreed, concluding that the check points were unconstitutional because the government interest was a traditional law enforcement interest rather than something else like public safety.

Even if it is constitutional, it's a rotten idea. But if it isn't, even more reason it should be scrapped.