[vfvawars] Drinking with intent to drive

The national drinking age of 21 is justified by drunken drivers on the road causing disruption to interstate commerce.

Consider a modification of the law which still preserves the spirit of the justification: a prosecutor must not only show under-21-in-possession, but also intent to drive while drunk.  "Intent to X" does exist for other prosecutions.

Thus, it would become difficult to prosecute college students drinking in their own dorms, especially on an urban campus where no one owns a car.

How to make this law a reality.