You have it turned backwards. The Constitution -- that document we started the country with, the one with the Bill of Rights, the guarantees of free speech, freedom of religion, right to carry firearms, etc -- is the essence of Liberalism, which means power derives from the People and government stays out of the way except where needed for things only a national institution can do. That's the definition, and it's always been the definition. This latter-day revisionism trying to redefine the term in order to score political points in some kind of demagoguery football game is bullshit.
That's what Billc is trying to do above by defining Liberalism as "classic" liberalism, which tries to put a foot in the door to suggest there's some other version. There isn't.