In order for Carter to win 1980, you need a few things. No Iran Hostage Crisis or a successful Operation Eagle Claw, or perhaps even the deaths of the hostages. Horrible as the latter is from a moral perspective, removing the matter as a lingering issue and being able to answer it through something blunt as a result, such as air strikes, may be enough. In addition, no Saturday Night Massacre, wherein Carter essentially fired his cabinet. The "malaise speech", as it was so called, was actually well received for its honesty. However, those firings threw Americans back into a mood that the country was out of control. Therefore, addressing those issues, you give Carter a competitive shot at 1980. You do not need a POD of Watergate or anything else like that. You literally simply need a competitive Carter who wins 1980.