muichimotsu
Holding All and None
What about it? That means if there is a conflict feds overrule, marriage has never been the federal governments responsibility. That's why it was always left to the states. Really the intention was to have the fed basically oversee the states and the states would act like countries of their own but still work together and agree on the federal governments conditions, not have all of them do whatever the federal government says with no questions asked.
There are some things the states cannot decide arbitrarily or even through some modicum of democracy, like civil rights that are imbedded in society or can arguably fall under the inalienable rights: life, liberty and the pursuit of happiness. As much as marriage could be construed as a privilege, the right to choose one's partner shouldn't be restricted based on a heteronormative idea of marriage and presented as "traditional", when it's far from that, historically speaking.
Supremacy Clause means the constitution is the law of the land, states and federal government are both beholden to it. The state doesn't get to override it with their state level constitutions.