Every state has one or several US attorney's offices with a number of US attorneys. Until they actually pass a federal law forcing them to honor the state laws, any one of them has the power to decide to prosecute under the existing federal statutes.
Really, the Constitution does prohibit them from over riding state law but legislatures have found ways around the issue by citing something called "the interstate commerce clause" which has historically been used with absurd vagueness.
Anyway, I don't see why people have difficulty understanding that Obama's only qualification for being President is that he is an articulate black man who appeases white guilt. Aside from that he has very little life or political experience and no real education save for being a lawyer and doing well at an ivy league college known for it's grade inflation and shameless promotion of black applicants and students that would otherwise fail to meet their criteria. Even his Senatorial election was obtained in a way that was less than Kosher. Obama is an uninformed and overly opinionated empty suit - that is all.