And that right there is what's wrong with American government right now. That's how we got Wickard v Filburn, Roe v Wade, Bowers v Harwick, and Kelo v City of New London. All bad law, all obviously unconstitutional, but all forced on us by the judiciary. It is very much incumbent on all three branches, and the American people, to decide what's Constitutional.
I think it's a fundamental flaw in our government. Yes, all three branches are at liberty to decide for themselves if something is constitutional or not, but they can't decide for the other branches.
So, for example, a president can veto a bill and explain that he did so because he finds it unconstitutional. Then the Congress can override the veto and say they think it is constitutional. The president can't stop them. The legislature may find the president exercising powers they find to be unconstitutional. What can they do about it?
And the court? They have the most awesome power of all! Not only can the other branches NOT overrule them, their decisions become law in a way that is much more likely to become fixed and permanent than anything the legislature or the president may do. When it comes to law, legislators legislate, executives execute, but the judges rule (no pun intended.)
It seems to me, this was by design. I believe Alexander Hamilton knew exactly what he was doing, and got what he wanted--a supreme court with a general tendency toward amassing national power at the expense of the states and/or the people.
The tendency of our scheme of three "co-equal' branches is not that no one gets away with extra-constitutional powers, but rather, that they all do. In fact it's a misnomer to call them extra-constitutional, since to me, the setup itself ensures just the kind of results we've gotten. The design is bad.