Part of yesterday's legal decision on Hazleton's enforcement measures focused on the question of how various state powers relate to various federal powers. Krikorian draws attention to a 2002 memo prepared by Jay Bybee (now a US Appeals Court Judge for the 9th Circuit) for then-Attorney General John Ashcroft. This memo has a number of typical Ashcroft themes about the inherent authorities of states vis-a-vis the federal government and attends to how much state governments may enforce immigration laws. There's some legal analysis in this memo that is interesting, but here's the conclusion:

(1) States have inherent power, subject to federal preemption, to make arrests for violations of federal law. (2) Because it is ordinarily unreasonable to assume that Congress intended to deprive the federal government of whatever assistance States may provide in identifying and detaining those who have violated federal law, federal statutes should be presumed not to preempt this arrest authority.

However, this memo has not been, Krikorian says, "formally published," and it's unclear how much influence it may have on upcoming legislative/judicial decisions. And many, including the ACLU, dispute this memo's reasoning and conclusions.