"It is emphatically the duty of the Judicial Department to say what the law is." - Marbury v. Madison.
Uhmmm...you might want to read the next sentence.
It is emphatically the province and duty of the judicial department to say what the law is. Those who apply the rule to particular cases, must of necessity expound and interpret that rule. If two laws conflict with each other, the courts must decide on the operation of each.
You do understand the difference between a claim to have all power to say what the law is generally and the power to say what the law is in particular cases, don't you?