Lets, for a moment take a look at the Federal Government, on behalf of the DOJ, DHS, DOS case against Arizona.
The Feds case is this:
The United States, on its own behalf and on behalf of the Department of Homeland Security, the Department of Justice and the Department of State, brings suit against the State of Arizona arguing Arizona law, SB 1070, as amended, is preempted by federal law and violates the Supremacy Clause of the U.S. Constitution.
But if we look at the paragraph in the US Constitution, article 6 (aka Supremacy) this is what it says, in plain, logical and coherent language (with key noted words).
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, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding.
Now where does it say that no state shall make laws pursuant to US laws.
It clearly states that Federal law is "Pursuant" to state law and that "Judges" in every State shall be bound thereby (first and foremost) by it.
This is why sanctuary laws in states can exist. However their sanctuary laws are null and void, as Federal law supersedes it.
But they enforce their laws with little to no challenge by the US Government.