"As Columbia University law professor Michael Dorf points out, the Supreme Court ruled in United States v. Nixon that, “where the President asserts only a generalized need for confidentiality, [executive privilege] must yield to the interests of the government and defendants in a criminal prosecution.”
Bush is invoking such “a generalized need for confidentiality,” according to a senior administration official this morning:
“This is not a mere exercise relating to a particular event. This is an exercise in an attempt to protect the prerogatives of the president for this president and for future presidents.”"
As I read this, the current administration has so abused the concept of executive privilege that it's future use is in doubt.