I am a little puzzled by Ed Whelan’s post below. That Congress can proscribe conduct in federal territories and was able to condition the admission of Utah and other states on the abolition of polgamy hardly establishes that marriage is or was a “federal” issue. By Ed’s logic, the federal government would have a plenary police power because it has such authority over federal territories and can impose nearly any condition on the entry of new states. Utah was required to create and maintain public schools as a condition of its entry into the union, but this hardly establishes a federal power to impose such requirements on pre-existing states or transforms public education into a federal issue. Like other aspects of family law, marriage has been a state matter except in those instances in which there is a clear federal nexus — such as interstate travel, presence in a federal territory, or the need to define a family unit for purposes of the federal income tax. On this point, I believe Rauch is correct.