"If you ask whether we learned anything, I would say not enough," says former U.S. Sen. Bob Graham, a Florida Democrat who opposed the war in Iraq, long after Tonkin and Vietnam.
In the last five decades, Tonkin has not kept Washington from backing wars, but it has shadowed relations between presidents and Congress. Debates about foreign conflicts, whether in Bosnia, Syria or Iraq, have also been referendums on trust. Is the war really necessary? Is the president telling everything he knows? What should be the parameters, if any, for military action?
Graham was chairman of the intelligence committee when the Senate debated, in the fall of 2002, whether to authorize military action in Iraq. Did Saddam Hussein, as alleged by the George W. Bush administration, possess weapons of mass destruction? Graham found the case "soft and unreliable" and voted no. But most of his colleagues disagreed. The Sept. 11 attacks were barely a year old, and the midterm election was just a month away, a difficult time to turn away the president or the Pentagon.
The Senate approved the Iraq resolution by 77-23, the House 296-133. A U.S.-led coalition invaded Iraq, opening a conflict that lasted for years. As Graham and others feared, the weapons were not found.
Former Sen. Max Cleland of Georgia, who had been badly wounded in Vietnam, was among those who supported the 2002 legislation. "I can't believe I volunteered for one war, which turned out to be a massive tragedy for the United States, and I went to the Senate and voted for another war, which turned out to be a massive tragedy," he says.
"It was right before my re-election and I felt compelled for my own hide," explains Cleland, who nonetheless was defeated. "It became the worst vote I made in my life."
Trust in the White House was high at the time Johnson signed the Tonkin resolution on Aug. 10, 1964.
Many at the time were haunted by the rise of communism. So-called Cold War liberals, recalling the difficulties President Franklin Roosevelt had a generation earlier gaining support for countering the rise of Nazi Germany, backed aggressiveness against communists overseas. One of the Senate's leading Democrats in 1964, Sen. J. William Fulbright of Arkansas, had three years earlier called for giving the president more leverage.
"I wonder whether the time has not arrived, or indeed already passed, when we must give the executive a measure of power in the conduct of foreign affairs that we have hitherto jealously withheld," Fulbright wrote in the Cornell Law Quarterly.
The Tonkin resolution was submitted and passed within 48 hours, its urgency heightened by the alleged attack and two other factors: Johnson was running for president against Barry Goldwater, the Republicans' most conservative candidate in decades, and U.S. involvement was steadily growing in the conflict between North Vietnam and the U.S. ally, South Vietnam.
Johnson's predecessor, John F. Kennedy, had increased the U.S. military presence in Vietnam from a few hundred advisers to more than 16,000. His assassination in 1963 left historians and former aides wondering what Kennedy might have done, if only because JFK expressed skepticism about success and reluctance to give up.
"In the final analysis, it is their war. They are the ones who have to win it or lose it. We can help them, we can give them equipment, we can send our men out there as advisers, but they have to win it, the people of Vietnam, against the communists," Kennedy said in an interview two months before his death.
"But," he added, "I don't agree with those who say we should withdraw. That would be a great mistake."
Like Kennedy, Johnson was conflicted about Vietnam. He believed in the "domino theory" of the Cold War, that one country's turn to communism would lead to the fall of others. He was also aware that the South Vietnamese government was unstable, at best, and that foreign policy experts had warned against sending land troops to Asia.
As Johnson saw it, he would lose no matter what. If he expanded the war, he would never fulfill his dream of building a "Great Society" at home, and the North Vietnamese could well still prevail. Let South Vietnam fight on its own, presumably in vain, and Johnson would be accused of surrendering to the communists.