J. William Fulbright came from a prominent family of politicians, and represented Arkansas in the U.S. Senate from 1945 to 1979. Being the Chairman of the Foreign Relations Committee of the Senate, he was an ally whose friendship Johnson needed to caress. Fulbright ensured the passage of the Tonkin Gulf Resolution, which gave the President extraordinary powers to wage war in Indochina.

However, Fulbright, sensitive to his constituency and distressed by the mounting American casualties, changed his mind regarding Vietnam. In 1966, Fulbright's Foreign Relations Committee held televised hearings on the Administration's policy in Southeast Asia.

Biography of J. William Fulbright
From the U.S. Senate web site
http://bioguide.congress.gov/scripts/biodisplay.pl?index=F000401