On December 20, President Trump signed legislation purporting to impose a single national age of 21 for selling tobacco products. Obviously, the measure reduces the freedom of millions of Americans who are legally adults in almost every other respect—including (correctly or not) the right to vote. Moreover, setting minimum consumption ages is not a power the Constitution grants the federal government. The Constitution reserves it to the states. The issue here, of course, is not whether tobacco products are safe. They clearly are not. The issue here is whether our Constitution and the...