None of the above.
The confusion arises because the word “federal” has a couple related meanings. 1. A federal system of government (also called a federalist system) is one in which there’s a nation made up of a federation of constituent entities (states, provinces, emirates, Lander, whatever – for simplicity I’ll just refer to them as states from here on), where some areas of law are under the dominion of the national government, and other areas are left up to the sttaes to decide for themselves and the national government has no right to gainsay it. For instance, in the U.S., family law is one major branch of law in the hands of the state governments. Virginia can’t tell Maryland that it should let 1st cousins marry; Maryland can’t tell Virginia that it should prohibit 1st cousins from marrying, and the national government can’t tell either of them anything on the subject. Other nations with a federal system of government may set the boundaries between national and state power differently, but the central idea of a federal system of government is that there are areas where the states can decide X and, if the national government wants them to do Y instead, they can tell the national government to fuck off.
Here’s the tricky part. 2. “Federal” can also refer to the national government in a federal[ist] system. So the U.S.'s federalist system means that power is shared by 50 states on one hand and the federal government on the other.
Looking back at the founding generation, everyone (well, not everyone, but for argument’s sake, let’s say everyone) agreed that there should be a federal (def. 1) system in the U.S. That is, power should be shared between the national and state governments, with each being supreme in its own spheres. The members of the Federalist Party were the folks who thought a strong national government was best – that is, they said, “Let’s put as much power in the hands of the national, a/k/a federal, government (def. 2) as we can.” They named their party after the level of government they liked the best.
When Sullivan uses the term federalism, OTOH, he isn’t saying he likes the federal government (def. 2), he’s saying he likes the idea of government as a federation of autonomous states (def. 1). So let some states do X and some do Y, and don’t let those dweebs in Washington have anything to say on the matter – because this is an area in which state law, not national law, is supreme.
Ergo, in this context federalism equates with states’ rights, because marriage is tradtionally a subject of state power in the U.S. But Federalism isn’t exactly the same as states’ rights, because adherence to federalism makes us overrule states when we’re talking about an area left in the federal government’s hands – like the income tax or commerce with foreign nations – just as we here overrule the federal government when it tries to butt in to an area traditionally reserved to the states.
OK, this is awfully redundant, but to boil it down further – today when we talk about federalism, we’re mostly venerating the two-tiered system itself. The Federalist Party was venerating one particular tier, which confusingly shares a name with the idea of the two-tiered system itself.
–Cliffy