Preemption and the U.S. government v. Arizona

Interesting article from Forbes that gives a nice conceptual vocabulary lesson in the term 'preemption', which is defined as "the idea that the federal government can 'occupy the field' of an area of law or regulation and prohibit lower governments from meddling with it." The tension between the Obama administration litigating this issue alongside its deportation policies that are nabbing even U.S. citizens is somewhat confusing.