Let's assume that Humphrey won California in 1968 (let's say there was more resentment in Nixon's home state), and as President Johnson above says, it went to the house. Despite only winning 236 electoral votes, HHH becomes president, although many people believe it to be illegitimate due to Nixon's electoral vote victory. The Democrats are fractured after their 1968 primaries, and southern Democrats defect to the Republican party, which makes major gains in 1970. Facing his third presidential run without a win, Nixon begins campaigning in 1970, and with such a close loss in 1968, he keeps Agnew on the ticket.
George Wallace, after an assassination attempt that left him paralyzed, does not compete in the 1972 election, and in a shock to the Democrat party, endorses Nixon. HHH follows public opinion and gradually reduces troops in Vietnam, but the GOP says it is too slow.
The end result is a comfortable win by Nixon, who doubles down on California and sweeps the south. (I gave Humphrey ever state that McGovern lost IOT by less than 20%)
