I thought that Obama was a Constitutional law professor in between his stints as a community organizer and a Senator

Chief Justice John Marshall

But apparently he hasn't read much Constitutional Law.  Perhaps the most important case ever decided since the adoption of the Constitution was Marbury v. Madison.  John Adams, an ardent Federalist, lost the election in 1800 to Thomas Jefferson.  Since Jefferson was not to take office until March of 1801, Adams and the lame duck Federalist controlled Congress passed the Judiciary Act of 1801, which tremendously expanded the number of members of the judiciary.  Adams quickly appointed 16 new Federal Circuit Court judges and 42 new Justices of the Peace--Federalists, one and all.  The Adams appointees were approved en masse by the Senate the next day.  However, in order to become effective, the appointments had to delivered to the various appointees.  Most were in fact placed in the hand of the newly named officials.  A few, however, did not get there before Jefferson took office.  And the new (most definitely NON-federalist) Secretary of State, James Madison refused to finish those deliveries.  Squire William Marbury, a Maryland Federalist financier had been appointed as a justice of the peace, but without his appointment in hand, he could not sit.  So he sued Secretary Madison, asking the Supreme Court to order him to carry out his duty.  Perhaps the greatest Chief Justice to ever don a robe, John Marshall wrote the opinion of the Court.  He held that Marbury had a claim and that it was remediable.  However, he stopped short of ordering Madison to give over the appointment (which Madison could have ignored since he and Jefferson had the army, and Marshall had naught but a pen).  Instead, Marshall found that the Judiciary Act of 1789, wherein Congress gave the Supreme Court jurisdiction to hear petitions of that nature, was unconstitutional because Congress had therein purported to convey to the Court powers that were beyond Article III of the Constitution.  Article III governs the judicial branch of government.  One has to wonder at what point in time during their celebrations did Messrs Jefferson and Madison realize they had been had.  Marshall seemingly sided with them and kept a Federalist off the bench.  However, the Court had firmly set the precedent that it was the final arbiter in the review of all executive and congressional acts to see whether they were allowed by the Constitution.  Thus was born the concept of judicial review.  So Mr. President, when you state that it would be unprecedented for this Court to strike down Obamacare as an unconstitutional exercise of power under the Commerce Clause, perhaps you should go back and dust off those law books.  The precedent was set over two centuries ago.