As the Attorney General, Eric Holder is the top prosecutor, not the top Justice. He  has no right to "declare" a law unconstitutional and therefore not worthy of defense.  If he is not willing to enforce the law, even ones he doesn't agree with, then he should step down.

So basically, he sues states that pass laws he doesn't like, he refuses to enforce federal laws he doesn't agree with...What part of his job does he actually do?