Why did the L.B.J. lie about the Gulf of Tonken?

Answer 1

That LBJ lied about Tonkin Gulf has never definitively been proven. However, if you want to assume for the sake of argument that he did, the answer would be that LBJ saw the imminent collapse of the South Vietnamese regime as catastrophic to America's interests in Southeast Asia.

At that time, American foreign policy was dominated by two Ideas: Containment and the Domino Theory. Under these two, it was believed that the US had to stop communism spreading in a reagion, or the entire region would become de-stabalized.

He believed that he absolutely had to involve America in the Vietnamese conflict or world communism would spread -- and he needed a pretext.

Answer 2

Which President doesn't want a blank check?

"The resolution was in fact a blank check, the amount of which the administration (LBJ's) itself had yet to determine. Congress would regret its actions only when it revised its opinions or after the administration's promises of action tempered with restraint had long since been broken. But to some extent Congress could conveniently claim a largely unjustified innocence, for the administration had indeed lied to Congress regarding the details of the Tonkin affair, obscuring the poltical fact that the policy had been drawn up much earlier, and had predetermined its responses. Above all, the White claimed it had been provoked when in reality it was the provoker."

Answer 3

to justify the Vietnam war.

Answer 4

to keep the money flowing