It is emphatically the province and duty of the judicial department to say what the law is. . . . If two laws conflict with each other, the courts must decide on the operation of each. . . . This is of the very essence of judicial duty.
Let the end be legitimate, let it be within the scope of the constitution, and all means which are appropriate, which are plainly adapted to that end, which are not prohibited, but consist with the letter and spirit of the constitution, are constitutional.