
The 1976 US electoral map is really unique in the twentieth century: Carter won no states in the western half of the United States except Texas and Hawaii--and both of those were close. Meanwhile, he carried the great majority of states east of the Great Plains (21-10). This was obviously made possible by Carter's near-sweep of the South and border states.
Challenge: *Not counting Carter getting re-elected in 1980* can you see a similar east vs. west map in the twentieth century? Of course there were what one might call "Bryanite" elections where the Democrats swept the West (e.g., 1916)--but they are not exactly 1976 in reverse because the Democrats swept the South.
Maybe the closest thing is 1960. JFK carried only four states in the western half of the country: Texas, New Mexico, Nevada, and Hawaii--and all of them were close.
But here is one other possibility I was thinking of: In 1952, Adlai Stevenson won nine states in the eastern half of the US, and not one in the western half. Perhaps if he were facing a Taft-Knowland ticket we could see a closer race with a 1976-like pattern. The seventeen states which Stevenson lost by less than twelve points in OTL were TN, MO, RI, DE, PA, TX, MA, OK, WA, IL, FL, NM, MN, MI, MD, CT, and NY.
https://en.wikipedia.org/wiki/United_States_presidential_election,_1952 Of these, only NM and WA were truly "western"--though TX and OK are im the western half of the US. Meanwhile, if he carried all these seventeen states, Stevenson would have carried 22 of the 31 states in the eastern half...