Following this pronouncement, many Conservatives took this as a sign that the Supreme Court's preliminary decision had been leaked, and that the President was performing damage-control. So jubilant were they about this, they forgot that Conservatives, too, believe that Supreme Court does not actually have the power to declare anything Unconstitutional. Some of them even went so far as to say this is what the founders "intended."
Let's take a look at that, shall we? Article III of the US Constitution establishes the Supreme Court of the United States. Section 1 of Article III establishes the courts. Section 2 grants its power. It reads:
"The judicial Power shall extend to all Cases, in Law and Equity, arising under this Constitution, the Laws of the United States, and Treaties made, or which shall be made, under their Authority; --to all Cases affecting Ambassadors, other public Ministers and Consuls;--to all Cases of admiralty and maritime Jurisdiction; --to Controversies to which the United States shall be a party; --to Controversies between two or more States; --between a State and Citizens of another State; --between Citizens of different States; --between Citizens of the same State claiming Lands under Grands of different States, and between a State, or the Citizens thereof, and foreign States, Citizens, or Subjects.
In All Cases affecting Ambassadors, other public Ministers and Consuls, and those in which a State shall be Party, the supreme Court shall have original Jurisdiction. In all the other Cases before mentioned, the supreme Court shall have appellate Jurisdiction, both as to Law and Fact, with such Exceptions, and under such Regulations as the Congress shall make.
The Trial of all Crimes, except in Cases of Impeachment, shall be by Jury; and such Trial shall be held in the State where the said Crimes shall have been committed; but when not committed within any State, the Trial shall be at such Place or Places as the Congress may by law have directed."
Now, I'm not a legal scholar, but nothing in there gives the Supreme Court Jurisdiction over the Constitution. The closest it gets is this clause, "...the supreme Court shall have appellate Jurisdiction, both as to Law and Fact..." but does this mean the Court gets to decide what Laws shall stand, and which shall not? The understanding at the time of Ratification was that it did not have that power. The court could decide the Facts of a case (that is, they could overrule any previous Finding of Fact), and they could determine what the Law said about the facts as established. They could not decide if the law itself was valid.
So what did the Founders intend? Well, they built checks and balances all across the system. The House was supposed to check the Senate, the Senate the House, the President both Chambers, and each of the Chambers the President. On top of that, the States themselves were supposed to be the arbiters of the Constitution. By the time something got to the Supreme Court, it was supposed to have been so thoroughly vetted that there wasn't really a question of Constitutionality.
Then, in Marbury v Madison, the Court unilaterally changed all of that- and the States, Congress, and President just let them. They claimed a power not explicitly given to them by the Constitution- in direct contravention of the Tenth Amendment which states: "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people." Since Constitutional Review was not "delegated to [the Court] by the Constitution," nor was it "prohibited by [the Constitution] to the States," Constitutional Review should have remained a power of the States.
So why not the Court? I mean, they're the biggest brains in the land, right? They have nothing to do but review law and the implications of same, right? Well... no. Many of the Justices who have served on the Supreme Court have been of relatively average intelligence. Moreover, there are simply too many laws for anyone to be familiar with all, or even most, of them. But even if those first two assertions were true, there are two major reasons that the Supreme Court should not have jurisdiction over what should be Constitutional.
The first of those reasons is this: the Federal Government was Established (Constituted) by the Constitution- that is, the Constitution defines and empowers the Federal Government. Why should the Federal Government be the one deciding what powers that document provides? As has been proven (Commerce clause, anyone?) the Federal Government will constantly broaden its definition of the document to give itself as much power as possible. That's just the nature of humanity.
The second of those reasons, however, can be more immediately shown: Justice Anthony Kennedy. Not him in particular- though that, too, at current- but the very fact that, at the end of the day, Supreme Court Justices are appointed for a lifetime, and are accountable to no one- with the exception of possible (but incredibly difficult) impeachment procedures. That being true, cases- sometimes even when they're very clearly cut-and-dried, will often be decided not by the Constitution's underlying principles, but by the Justices' philosophical leanings. That means decisions which are vitally important to the operation of the United States, and the Liberty of the People, will come down to one man (or woman). When that is true, that single man or woman is, in effect, a Monarch, ruling over subjects- not a Public Servant, upholding the Public Trust.