Excerpted sections from the US Naval Institute's website
https://www.usni.org/magazines/naval-history-magazine/2008/february/truth-about-tonkin
To enhance his chances for election,[Johnson] and McNamara deceived the American people and Congress about events and the nature of the American commitment in Vietnam. They used a questionable report of a North Vietnamese attack on American naval vessels to justify the president's policy to the electorate and to defuse Republican senator and presidential candidate Barry Goldwater's charges that Lyndon Johnson was irresolute and "soft" in the foreign policy arena.
These new documents and tapes reveal what historians could not prove: There was not a second attack on U.S. Navy ships inthe Tonkin Gulf in early August 1964. Furthermore, the evidence suggests a disturbing and deliberate attempt by Secretary of Defense McNamara to distort the evidence and mislead Congress.
We may never know the whole truth behind the Tonkin events and the motivations of those involved. However, it isimportant to put what we do know into context. The administration's zeal for aggressive action, motivated by President Johnson's election worries, created an atmosphere of recklessness and overenthusiasm in which it became easy to draw conclusions based on scanty evidence and to overlook normally prudent precautionary measures. Without the full picture, Congress could not offer the checks and balances it was designed to provide. Subsequently, the White House carried the nation into the longest and one of the most costly conflicts in our nation's history.