The U. S. Supreme Court ruled that a California law barring the hiring of illegal aliens was not preempted by federal immigration law. http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&vol=424&invol=351 It's hard for me to see how this Supreme Court decision is not directly on point and controlling. Arizona is clearly not doing anything inconsistent with federal law. At base, obama is arguing that the Arizona law should be preempted because he doesn't want to enforce the federal law. That should be grounds for impeachment, not preemption.
So I suppose you are in favor of prosecuting all of the cities and municipalities that have declared themselves sanctuaries right? Because of course it's about the Constitution not about vote pandering or some faculty lounge vision of "social justice".
+1 Arizona law should be preempted because he doesn't want to enforce the federal law, thereby pandering to the Hispanic vote.
Democrats are all for immigration "reform" and claim to be against illegal immigration. Oddly however, they find reason to oppose every single proposal to enforce the law, from border fences to raids to troops on the border to the Arizona law. It's kind of like how they "support the military" and are for "lower taxes" and against "vote fraud", yet in every case their actions belie their claims.