Howard Baker? Bob Dole? Phil Crane? Bush would be too junior at this point, so one of them wins over Sanders/Sanford in 1976. If the economy goes in 1980 then it depends who the Democrats nominate. So if Bentsen won in 1970 then he might be the nominee with not-so-covert Kennedy backing, and if Bush wins it is anyone's guess. Probably a liberal, maybe even Ted, though I doubt it. If the GOP wins in 1980 then you might get Hart v. Bush in 1984.