In February, the day after his infamous encounter at Washington’s Mayflower Hotel, Eliot Spitzer, then the governor of New York, published a remarkable opinion piece in The Washington Post.

He wrote that several years earlier, state attorneys general noticed a spike in predatory lending that the federal government was doing nothing about. When the states tried to rein in abusive mortgage lenders, the Bush administration finally did something. The Office of the Comptroller of the Currency issued rules nullifying state predatory lending laws over the objection of all 50 state banking superintendents.

The clampdown, which paved the way for the subprime mortgage crisis, was done by “pre-emption,” a little-understood doctrine that allows the federal government to wipe away state laws. The Constitution’s supremacy clause says federal law can trump state law. But the federal rule should be a floor, not a ceiling. It should set a minimum level of rights, not stop states from doing more to protect their citizens.

For years, the federal government used pre-emption in this way. Civil rights acts swept away discrimination at the state level, and workplace safety laws upgraded conditions in factories and mines. Conservatives opposed many of these federal laws on the principle that they were trampling on “states’ rights.”