Revisionist historians of the Vietnam War--like Guenter Lewy, William Colby, Lewis Sorley and Mark Moyar--challenge the prevalent view that US military intervention to sustain the non-communist regimes in South Vietnam, Laos and Cambodia was a lost cause. In other words, they believe the Vietnam War was winnable if certain key mistakes were not made by the USA (i.e, overthrow of Diem in November 1963) and a different war strategy (i.e, closing the Ho Chi Minh Trail, emphasis on anti-insurgency and rural security) was pursued by the US beginning in 1964-65.
What if the US had steadfastly supported Diem, instead of encouraging the South Vietnamese Generals' coup against his regime in late 1963? What if the US had introduced substantial ground forces in early 1965 for the express purpose of enforcing a demilitarized zone along the 17th-parallel from the sea through Vietnam and Laos, thus permanently cutting the Ho Chi Minh Trail supplying communist forces in the South (like the 38th parallel along the Korean peninsula)? What if the focus of the US and South Vietnamese war effort beginning in 1965 was anti-insurgency and rural security, behind the screen of static US forces along the 17th parallel keeping new communist fighters and supplies from funnelling down from the North into the South? Could a stable Korean-style "cold peace" have taken hold that would have lasted well-beyond 1975 and perhaps to the present day?