People who talk about the 'protesters' beating America in Vietnam have misunderstood as completely as Brezhnev did.
In December, 65, LBJ's economic advisers flatly told him that he could have three of the following four things.
1. A major increase in domestic spending (i.e., Medicare, War on Poverty).
2. A major war.
3. No tax increase and therefore a booming, full employment economy.
4. No inflation.
LBJ tried to have it all. And because of this inflation started to take off in the late 60s and surged to 10% plus well before the oil crisis. That's the level at which people on fixed incomes are going to be screaming bloody murder. Nixon had to end inflation. Economically, a perfect storm situation was brewing because this coincided with the emergence of Japan as the primary exporter and the entry of the main cohort of the baby boom with their worthless liberal arts BA's into the work force, depressing entry level salaries from 60's soaring levels. He pursued deflationary measures, abandoned the Bretton Woods "gold standard", and decided to get out of Vietnam. The reasons for getting out of Vietnam were economic, not political.
After all, if the peace movement was so powerful why wasn't it the dominant political force of the 70's and 80's ? Why couldn't it put McGovern into the White House or keep Reagan out ? Once horror stories about college graduates parking cars or waiting on tables filtered back on campus, didn't the counterculture and the student left collapse pretty quickly ?
Brezhnev thought it was the peace movement. He therefore decided to put the Soviet Union on what amounted to a total war footing to build a military that would intimidate a craven West. He poured vast sums into Soviet proxy states in Africa and Asia. He built a huge blue water navy from scratch. He made a mistake that ran the Soviet economy straight into the ground because he overestimated Western pacifism and defeatism. One might say that the decisive battle of the Cold War was over deploying the Pershing missiles and the reelection of Reagan, Kohl, and Thatcher and the total defeat of the European and American no-nukes protesters.