Genesee County, Michigan Sheriff Robert Pickell is not concerned about the constitutionality of his new method of keeping Flint free of illegal drugs. Fourth Amendment fans, medical marijuana patients, and jumpy motorists are less sure.

According to the Detroit Free Press:

At least seven times [in October] motorists have said they have seen a pickup towing a large sign on I-69 or U.S.-23 that depicts the sheriff's badge and warns: "Sheriff narcotics check point, 1 mile ahead—drug dog in use."

The checkpoints are part of a broad sweep for drugs that [Pickell] and his self-titled Sheriff's Posse said are needed, calling Flint a crossroads of drug dealing because nearly a half-dozen major roads and expressways pass in and around the city. Pickell said he decided to try checkpoints when he learned that drug shipments might be passing through Flint in tractor-trailers with false compartments.

After some outcry, Pickell's posse have begun making these checkpoints more sporadic. Pickell also admits to using drivers' reactions—say, nervous, illegal U-turns– to the warnings as a pretext for pulling them over anyway.

Pickell won't confirm if anyone has been arrested. He says he welcomes a chat with the American Civil Liberties Union over the matter.

The Michigan Supreme Court ruled in 1990 that DUI checkpoints were illegal, but the U.S. Court leaves the matter up to the states, under certain conditions. And:

Based on a case out of Indianapolis, the U.S. Supreme Court held in 2000 that narcotics checkpoints where everyone gets stopped on a public road are not legal and violate Fourth Amendment protections against illegal searches and seizures, professor David Moran at the University of Michigan Law School said.

Wayne State University Law School professor Peter Henning said police can set up roadblocks to search all who pass by, but only if a crime has just been committed.

So far nobody has challenged the tactics in order to test their constitutionality. Sheriff Pickell's personal analysis will have to do for now.

Reason on DUI checkpoints (and the nemesis of Democrat New York Sen. Chuck Schumer, DUI checkpoint phone apps!) and the Fourth Amendment.

Also, Radly Balko and Greg Beato on the excessive trust placed in drug dogs (the use of which, according to a 2005 Supreme Court ruling, somehow do not constitute a search).