One point of clarification: DHS already conducts random car searches at road blocks. These "border" inspections occur tens of miles (often over 100 miles) inside our borders. TSA VIPR teams have searched bus passengers, train passengers, and cars. Here's the relevant passage from the WaPo article, in which the reporter appears oblivious to this fact:
Supporters of the TSA's more aggressive screening measures are quick to point out that no one has to fly, and that Amtrak, Greyhound and personal vehicles are still available.
But similar security searches are now being conducted on trains and in other public areas, including random screenings of Metro passengers in Washington, as well as mass-transit riders in New York and Boston.
The TSA has also indicated that it wants to move the perimeter of aviation security screening beyond the airport, to checkpoints on the road, according to Chris Calabrese, an attorney for the American Civil Liberties Union. If these roving searches are tolerated within the terminal and are allowed to jump to the street, there's no telling what might come next. It isn't inconceivable that in the near future, the TSA could set up roadblocks to randomly screen automobiles anywhere it pleases.
And if the TSA is permitted to expand its screening, it could prompt further outcries from the traveling public and more comparisons to a police state, say Calabrese and other privacy advocates.