I love how President Obama calls this law "irresponsible." I know that even to some conservatives provisions of this law seem extreme. But what many people don't realize, apparently Obama included, is that Arizona's border with Mexico has become a lawless region where American's aren't safe in their own homes.
This law sets up a very interesting dynamic; if democrats suddenly front-burner national legislation in response to this that essentially means amnesty, it'll put Republicans running for Congress this fall in a position where they can support Arizona, or fall somewhere between this law and what Democrats will be pushing. Admittedly, as stated above, much of America doesn't realize what illegal immigration has done to Arizona, so liberals will try have an opportunity to paint this as extreme. It'll be up to Republicans to educate the rest of the country on this issue.