re: out on a limb
The antiwar protestors were a symptom, not a cause. Nixon, a virulent anti-communist, had been on the Left's political hit list for a very long time, and the reaction to his defeat of McGovern, who symbolized all that the Left hoped for in government, got pretty much the same reaction from the Left as Bush's election victories did.
Nixon's massive screwup gave them the opportunity they needed.
For the record, I'm no fan of Nixon, either back then, or now.