Did Republican troubles in the north start in the 70's?

[Orser67]

You could arguably go all the way back to 1928, when Democrats won Rhode Island and Massachusetts despite losing the popular vote by 17 points. Since that time, Republicans have gotten weaker and weaker in the Northeast (compared to the rest of the nation). But if we're going to use a more recent date, in 1968 Humphrey carried much of the Northeast despite losing the election. Republicans were still competitive in the Northeast until the 1990s, but Democrats generally did better in the region than in the rest of the country (except in 1976).

[Orser67]

Ford, as a person, had a regional appeal to the north.

I'd imagine Carter also was probably relatively unappealing for a Democrat, being an evangelical from the Deep South