Forty years ago, President Richard Nixon, backed into a corner by the Supreme Court, surrendered Watergate's "smoking gun" tape. Recorded six days after the break-in at Democratic National Committee headquarters, it revealed the president scheming to get the CIA to quash the investigation — making it clear that he was in on the cover-up from the start. When Nixon was out, Gerald Ford called it a "national nightmare." Get real, writes Gene Healy. Four decades on, it's clearer than ever that Aug. 9, 1974 — when Americans finally dethroned an imperial president, and began reining in the imperial presidency — is a day worth celebrating.