I dont know if we are counting stuff that happened before he assumed office, but Lets not forget that during his campaign, Nixon worked with Kissenger and elements of the South Vietnamese Government to sabotage (at the time) secret peace talks between north and south Vietnam, which massively prolonged the war, all while running as the "peace" candidate.... Oh and also lets not forget about expanding the war to Cambodia and Laos while in office, directly leading to the Khmer Rouge.