Were Massachusetts African Americans the first to re-align ?

[Southern Senator North Carolina Yankee]

I doubt this reached down to the mass of voters, but there were certainly many periods of disillusionment, especially as subsequent generations of leaders got tired of the GOP resting on his laurels and not really doing much if anything.

This is why even Wilson got WEB Dubois for instance, though he later regretted supporting him obviously. Obviously that was decades later.

[Southern Senator North Carolina Yankee]

I am not sure, but I do recall seeing one time that Northern Blacks self-identified as Republicans at a 60/40 rate (in a two-way split with Democrats) by the 1880s ... that is obviously MUCH earlier than conventional/lazy political narratives of them being reliably Republican until the Progressive Era.  So, given Massachusetts was a state with relatively little racial tension compared to other areas of the country, this would not surprise me.

On another somewhat related note, I also recall seeing that the Southern Blacks who could vote remained more Republican than their Northern counterparts for longer, possibly even voting plurality for Eisenhower in many areas.

I would be curious to see if these margins widened with WJB on the Democratic ticket, or narrowed? I could see reasonable justifications for it going either way in this regard.

[Southern Senator North Carolina Yankee]

With so many racist and segregationist Southern Democrats in the party, I imagine many black voters looked to the Republicans, or that the idea that you were a Democrat wasn't passed down by your parents and grandparents so it there wasn't any affiliation in the family with the Democrats.  There were probably many that didn't trust either party to really advocate for black people.

I know that Philadelphia was once very Republican (with a machine running the city) and there were probably a lot of black votes for Republicans there.

As for Massachusetts, all I know is Edward Brooke.
Edward Brooke was an African-American Republican U.S. Senator from Massachusetts from 1967-1979.  I would be curious to how African Americans in Massachusetts voted in 1966, 1972, and 1978.

Consider also that we taken for granted that if some politician makes a comment or something, it is national news. Back then, what Democrats were doing in South Carolina or Florida, likely wouldn't have had as much impact for lack of TV, radio, 24hr news cycle, smart phones. This meant that there would be a consideration to "local party members" over and above what the national party was traditionally associated with.

This applies writ large and is a large part of the reason for the rise of polarization in the modern era, communication and media.

[Southern Senator North Carolina Yankee]

I am not sure, but I do recall seeing one time that Northern Blacks self-identified as Republicans at a 60/40 rate (in a two-way split with Democrats) by the 1880s ... that is obviously MUCH earlier than conventional/lazy political narratives of them being reliably Republican until the Progressive Era.  So, given Massachusetts was a state with relatively little racial tension compared to other areas of the country, this would not surprise me.

On another somewhat related note, I also recall seeing that the Southern Blacks who could vote remained more Republican than their Northern counterparts for longer, possibly even voting plurality for Eisenhower in many areas.

I hypothesize that this was in part due to the following reasons

1. The state- and local-level Republican Parties in the South (excluding Appalachia and perhaps also the Ozarks) were, to a large extent, organizations that essentially existed for the primary purpose of being pro-Black social, cultural, and political institutions - of, by, and for Black people. This was not the case at all in the North (save perhaps for some Black-majority areas within certain major cities such as Chicago and Philadelphia, as well as some of the small number of rural Black communities in the North, such as Pembroke Township IL, Alexander County, IL, or Eastern Shore counties in Maryland).

2. White supremacy/White racial interests were a key component of the Democratic Party platform in the South relative to the Republican Party in the South - further cementing the popular conscious and subconscious understanding of the Republican Party as innately being the intrinsically "Black party" (similar to de-facto status of the Democratic Party today as, unfortunately, being the intrinsically "Black Party" in most places post-1964) - whereas this was not nearly as true (but still definitely true at all) of the Democratic Party in the North relative to the Republican Party in the North.

3. The "60-40" figure, which is featured in the Wikipedia's article on the Third Party System (which is where I first saw the figure before I read your post, and where I imagine you have seen the figure if not also from someplace else) is a figure (estimate? canvass?) that comes from a book, The Third Electoral System 1853–1892 (1979), by an author named Paul Kleppner (as sourced in the Wiki article). Before World War I and the contemporary "Great Migration," the large majority of Northern Blacks were disproportionally college-educated, high-school graduated (to the extent that was an applicable category back then), upper- or upper-middle-class, higher-income, and (I would wager) ideologically left/liberal-leaning relative to the Southern Black population and to the Black American population as a whole; therefore, they almost certainly were much more likely Dem voters than the Southern or Nationwide Black population at the time.

I know a few folks who would and might freak out after reading this.