For one, I doubt, given how poorly he campaigned in '72, that HHH would ever have become President on his own had JBJ not died in office (12-14-71).
1972 PRESIDENTIAL ELECTION:
Ronald Reagan & John Volpe - 288 E.V. & 50.8% P.V.
Hubert Humphrey & Terry Sanford - 250 E.V. & 49.2% P.V.