OK, I'm thinking that a useful step would be to have a US president determined/suicidal enough to bomb North Vietnam again as punishment for its aggression. So I'm thinking of 3 options:
1) Watergate goes different and Nixon doesn't resign, or at least resigns later than in OTL. Would he react more strongly to the North Vietnamese than Ford?
2) Spiro Agnew avoids his trouble with the law and succeeds Nixon. Same question as above.
3) Nixon picks someone else as vice president. What people were both likely to be picked and more hawkish than Ford? John Connally?
1) Oh yeah. Watergate IOTL cut off American funding, weapons, and air support to South Vietnam. Nixon would have no problem in kicking Rolling Thunder off again and—combined with continuing guns/money—that would likely be enough for the South Vietnamese to win again.
2) Nobody liked Agnew, not even the Republican base. He either gets tossed or loses in the '76 primaries (to Reagan).
3) He wanted Connally but Congress wouldn't confirm with Watergate. If our POD is Nixon runs a clean '72 campaign (or that Watergate is never investigated) but Agnew goes down he probably has a freer hand and could get Connally.
Connally poses an interesting question for '76 of course—Will Reagan narrowly lose as IOTL to Ford, or will Reagan narrowly beat him?
(@Grey Wolf. Rockefeller doesn't fit in with Nixon's basically correct understanding of intra-party Republican politics, although at least on Viet Nam he would likely serve Nixon's purposes.)