Guess what? The voters of the State of California authorized him to do this when they passed Prop 215.
Do you have a problem when a majority of voters pass laws in their own state, Mr. Federalist?
Do federal laws trump state laws, Mr. I-Don't-Know-or-Care-About-The-10th-Amendment?
Not if they're constitutional laws. Do you support voters in a state passing unconstitutional laws, Mr. Anarchy?
"Do federal laws trump state laws, Mr. I-Don't-Know-or-Care-About-The-10th-Amendment?
Every time. It's called the Supremacy Clause, found in Article VI of the U.S. Constitution.