Good for him. We need more men with guts to stand against federal tyranny.
"This Constitution, and the Laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States,
shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the constitution or laws of any state to the contrary notwithstanding."
Amendment X
The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.
Now, where is the power to define marriage delegated to the federal government in the Constitution? Post the exact quotation.
As you put the 10th amendment on point, let's break it down:
"The powers not delegated to the United States by the Constitution"
The 14th amendment guarantees "Equal protection under the law" and applied that right to the states. It is a power delegated to the United States by the Constitution. Therefore, it's not a "states rights" issue, this is a power in the Constitution for the United States. Pesky Founding Fathers and their Article 5. I guess they aren't true Americans.
"where is the power to define marriage delegated to the federal government in the Constitution?"
The issue isn't "defining marriage" as you put it. The issue is that there are laws on the books in states that grants the right of marriage to citizens of their states. Now, a group is being classified as unworthy of that right.
When that occurs, the courts can apply 3 tests. Strict Scrutiny, Intermediate Scrutiny and Rational Basis tests.
In all gay marriage cases, the Rational basis test is the only one being applied since the court determined (wrongly IYAM) that Gay people do not have a history of "animus" towards that group. All these governments have to prove is that the classification has some "rational basis" to a "legitimate government interest". This is literally the lowest standard that must be met and 95% of the time, the government cannot come up with a legitimate government interest as to why this classification must exist.
That's why this issue is a loser. There is no legitimate government interest in denying two consenting adults the right to marry.