Why did the Northeast swing to Johnson in 1964?

[Mr. Smith]

Looking at the results of the 1964 election, I am astonished by how strongly Lyndon Johnson did in the Northeast that year. As we know, the Deep South moved to Barry Goldwater because of civil rights. But was that the reason why states like New Hampshire, Vermont, and Maine, Republican strongholds at that time, moved to Johnson? Especially the latter two, which had never voted for Franklin Roosevelt. Why did they support Johnson so strongly? And why did he do so well in New York, Massachusetts, and Rhode Island (besides the fact that these are Democratic-leaning states)?

Yes, that's exactly the reason.  As for MA and RI, they were far opposed to reactionary economics and strong benefactors of the New Deal.

The better question is, why were California and Illinois so weak? Did Pierre Salinger create reverse coattails against LBJ? Was homeboy Nixon's campaign somewhat resonant in SoCal?  And why was Utah further left than Idaho [the reason Arizona was farther right than Utah was obviously the native-son effect] that year?

[Mr. Smith]

Looking at the results of the 1964 election, I am astonished by how strongly Lyndon Johnson did in the Northeast that year. As we know, the Deep South moved to Barry Goldwater because of civil rights. But was that the reason why states like New Hampshire, Vermont, and Maine, Republican strongholds at that time, moved to Johnson? Especially the latter two, which had never voted for Franklin Roosevelt. Why did they support Johnson so strongly? And why did he do so well in New York, Massachusetts, and Rhode Island (besides the fact that these are Democratic-leaning states)?

Yes, that's exactly the reason.  As for MA and RI, they were far opposed to reactionary economics and strong benefactors of the New Deal.

The better question is, why were California and Illinois so weak? Did Pierre Salinger create reverse coattails against LBJ? Was homeboy Nixon's campaign somewhat resonant in SoCal?  And why was Utah further left than Idaho [the reason Arizona was farther right than Utah was obviously the native-son effect] that year?

I do find that interesting. Idaho was Johnson's closest win, while he won Utah by nearly ten percentage points. Why were Mormons turned off by Goldwater, considering Arizona is Utah's neighbor also?

Arizona had the native-son effect, and even then was the narrowest loss.

But this is the first election since then that Utah's been more Democratic than Idaho.