A very interesting story on the BBC which is based on newly declassified white house recordings from 1968. It seems that the framework for a peace deal in Vietnam was lined up before the 1968 election. On the day it was to be announced, South Vietnam pulled out, extending the war for another 5 years.
It turns out that Nixon, fearing a pre-election peace would sink his chance to be president, secretly and illegally contacted the South Vietnamese and told them to withdraw, promising them a better deal if he was elected.
LBJ knew because the FBI had bugged Nixon, but believing they would win the election anyway, said nothing publically. Nixon won by 1%.
BBC News - The Lyndon Johnson tapes: Richard Nixon's 'treason'
How history could have been different...