What really happened in the Gulf of Tonkin in 1964?

Historians still argue about what exactly happened in the Gulf of Tonkin in August of 1964. What's not in dispute is the aftermath: A resolution from the Senate passed by a vote of 98 to 2 authorizing President Lyndon Johnson to use whatever force he thought he needed against North Vietnam. The resolution was a major escalation of US involvement in Vietnam and helped Johnson win the presidential election. But it was built on a lie.