I understand what you're saying, Dave (i.e. Supremacy Clause), but to be fair, it's not actually cut and dried. On either side. (as in during Obama's term) 
Nice quote from the Congressional Research Center:
"The ability of state and local police to make arrests for federal immigration violations is a subject of legal debate and conflicting jurisprudence. Traditionally, the prevailing view has been that state and local police are permitted, to the extent allowed under state and local law, to enforce the criminal provisions of the INA. By contrast, the enforcement of the civil provisions, including the apprehension of deportable aliens, was viewed as a federal responsibility, with state and local police playing, at most, a supporting role. "
http://trac.syr.edu/immigration/library/P5028.pdf
It's not hard to make a state's rights argument from either side of the immigration issue. In other contentious areas, pushback at the local level has led to clearer legal definition (either pro/con)