So Reagan beats Kennedy in '76- does Reagan avoid the troubles that plagued Carter?- does he get reelected in 1980? Even if Reagan has coattails, the Dems are still gonna have at least 55 senators(unless Reagan is catalyst for a truly incredible landslide. Even then I can't see the Republicans winning a majority in the senate).
I've got a feeling that Reagan dodged a bullet by not winning is '76. Certainly he would have been a better president then Carter, but 1980 would have been a hard year even for a ressurected George Washington or Lincoln

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And even if he had overcome the obstacles Carter failed to deal with and won 1980, his presidency wouldn't have been such a conservative milestone, purely because of the strong Democratic position in congress- contrast that with their position in real history when he won in 1980, where the Republicans had gained a majority of 53 in the senate.