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
POTUS has no power to execute an unconstitutional law
1. I said "Where does it say he doesn't have to [enforce a law] if it violates the Constitution?"
2. You pasted the 10th amendment - This says the federal government has the powers specified by the constitution and any power not mentioned are for the states unless prohibited
3. Then I asked you how this related to the president not enforcing laws he believes are unconstitutional and you said "If the "United States [government]" doesn't have the power, POTUS in his official capacity doesn't."
The Constitution says the president has a duty to execute the laws.
Where does it say he doesn't have to if it violates the Constitution?