The Wall Street Journal's indispensible editorial writers today remind everyone whose memory only goes back as far as 1974 that once upon a time, the federal government did engage in unconstitutional, warrantless surveillance of Americans. It was carried out by J. Edgar Hoover, with the knowledge and complicity of presidents, congressmen, senators, representatives and judges from the FDR administration until Hoover's death in Nixon's administration.
Note that when we refer to "knowledge and complicity," we don't mean oversight. Hoover dug up scandals about politicians and threatened to expose them if they tried to remove him as FBI director. Then he offered to share information that they'd find interesting.
In his magesterial biography of Harry Truman, David McCullough notes that FDR took salacious delight in reading Hoover's briefings on the peccadillos of various senators and judges. Truman, by contrast, refused to read Hoover's dirt, though he also did nothing to stop Hoover's activities. Presidents thereafter accepted Hoover's mess as part of the cost of doing business.
By contrast, the Bush administration's surveillance is (a) done with the knowledge of the Senate Intelligence Committee and the FISA court; (b) directed at people making contact with known al Qaida operatives overseas; (c) not connected in any way to any purely domestic crimes or political matters of any kind.
Moral: those ignorant of history are likely to exaggerate the significance of the present.