The Gulf of Tonkin incident -- in which North Vietnam purportedly attacked U.S. destroyers -- was used to get to the U.S. into Vietnam. We all know how that war turned out.
Fast forward to 2002, when a internal investigation found that NSA officers deliberately skewed intelligence to conclude that North Vietnam was responsible. No massive surprise there, but check out what came next:
The NSA historians tried to go public. Today's NY Times reports:
But their effort was rebuffed by higher-level agency policymakers, who by the next year were fearful that it might prompt uncomfortable comparisons with the flawed intelligence used to justify the war in Iraq, according to an intelligence official familiar with some internal discussions of the matter.