Or alternatively, had the US bombed Cambodia earlier in the war, when, say, LBJ was in power in 1968, the North Vietnamese might not have overrun the South Vietnamese after the American pullout, and Prince Sihanouk might not have been vulnerable to the Khmer Rouge in the first place.
One could also make the case that if anybody has the blood of the Cambodian people on their hands, it would be the congress during the Ford presidency, which cut off all aid for the South Vietnamese, allowing the North to prevail, and the follow on events in Laos and Cambodia to happen without intervention.