Sanctuary Cities Violate Supremacy Clause

It has always fascinated me that the liberal left progressives regularly use the Supremacy Clause as an excuse for the unconstitutional control the federal government wields over the States, but when the Supremacy Clause is actually violated, they suddenly ask about States' Rights and disregard the presence of the Supremacy Clause in the U.S. Constitution. President Obama used the Supremacy Clause against Arizona S.B. 1050, that State's immigration law, saying that if the federal government chooses not to enforce immigration law, as per the Supremacy Clause, the States cannot have laws contrary to that federal inaction. Never mind that in Article II, Section 3 of the U.S. Constitution the President is instructed to "faithfully execute the laws of the United States."