My long-ago colleague Norman Leahy, once a young research assistant at the Cato Institute, has an op-ed in the Washington Post today. I wonder where he got the idea that an act of the legislature is invalid just because it violates the state constitution.

Those praising the Virginia General Assembly’s transportation compromise may not realize that the bill runs afoul of the plain language in the state’s constitution.

Virginia’s constitution is clear that the General Assembly can impose only uniform taxes across the state for similar activities. But the bill that emerged from the House-Senate conference committee last weekend upsets the historic balance between localities and state government; it contains new provisions about taxation, some of which would effectively set up a two-tier system for residents in certain parts of the state. It’s difficult to see how some of these provisions could survive legal challenge.…

As a constitutional matter, these local tax provisions could probably be struck down without affecting the rest of the legislation.

But few should know better than Gov. Bob McDonnell (R) that state legislators don’t have the power to impose a discriminatory local tax. He was the state’s attorney general when his office defended before the state Supreme Court the General Assembly’s previous attempt at a transportation tax package. The court rejected the argument.