We had half a million troops in Vietnam. We never has a tenth that many in Afghanistan. Nixon's plan was not actually put into effect, since the US did not leave according to Nixon's plan. Remember that Nixon was driven from the White House before the US left Vietnam,and that the US was driven out of Vietnam. They were FORCED OUT. Nixon took office in January, 1969. The last troops were driven out by the NVA in April, 1975. Nixon may or may not have planned to stay even longer than that, but he had over SIX YEARS.
It has not taken Obama SIX YEARS,and we are not being driven out, either.