How did Vermont go from being the most Republican state to the most Democratic

[All Along The Watchtower]

Vermont was a very "Yankee" state for a long time (centuries, actually), which meant heavily moralistic Protestantism and the kind of reformist public life and politics that followed from that. There was more than a tinge of anti-Catholicism in this Protestant moralism, in addition to being virulently opposed to Southern slavery/rebellion, or anything that sought (or was perceived as such) to undermine the Union. In that sense, Vermont and other strongholds of Yankee/New England Protestantism - perhaps more than anywhere else - identified their own values as being equivalent to the nation's values.

Today, Vermont is considerably more pluralistic and secularized than what it used to be, with plenty of Catholics, Jews, and other types who, in the 21st New England context, are very liberal (and who the remaining Protestants have accommodated, even as New England Protestantism has changed in many ways to be more pluralistic and less "evangelical" ), but it still retains a lot of that core Yankee/New England Protestant moralistic cultural influence on its politics. It's the interactions of Vermont's long-established cultural traditions with the added influx of newcomers that makes it, in contemporary terms, one of the most "liberal" places in the country.

[All Along The Watchtower]

The parties switched platforms.

I don't know you well enough to know if you are typing that ridiculous sentence sarcastically or not, but the troubling thing about that myth is that it's so comforting to several different groups.

It is a nice comforting narrative to modern-day liberal Democrats, as (in their minds) it absolves the party of any racism in its past, all the while stealing any Republican accomplishments on the matter and forking it right over to the endless, always-right social treadmill of "liberalism."

It's comforting to Black voters, as it completely justifies the demographic group's switch from the GOP to the Democrats.  It's a lot more noble in the history books to paint it as the GOP turning on Black voters one day in a spat of coded racism than Blacks being forced to vote their economic interests three decades before the CRA/VRA.

It's also pretty comforting to Southern whites, as they can justify their ancestors' (whom they otherwise seem quite proud of) support of an openly racist party by hiding behind things like "states' rights" or "small government."  Of course, things like the Dred Scott case show that Southern Democrats didn't give a crap about states' rights and were willing to take any avenue possible to preserve White racial supremacy.

That pretty much just leaves Northern Republicans and Democrats who are true students of history/not completely ignorant (which, I'll say, describes most on this forum) to try to refute this fairy tale and tell the much more complicated story.

The Democratic Party was openly hostile to blacks until the FDR years.  This was, in no small part, because in the South, most states did not allow blacks to become memberes of the Democratic Party.  This was not true in every state, but it was true in many, and the "White Primary" lasted until 1944 when the SCOTUS threw it out.

In truth, it was the Nixon years that drove blacks out of the GOP in any kind of significant numbers.  Goldwater ran them off with his Civil Rights stances, but Nixon kept them gone with a Southern Strategy that sided against blacks whenever they were in conflict with the White South.  As late as the mid-1960s, Everett Dirksen and Gerald Ford were producing GOP votes to ram home Civil Rights legislation, but this all stopped during the Nixon years.

At the end of the day, no Republican has won the Black vote since HERBERT HOOVER.  That's a long while before Richard Nixon.  Eisenhower, post-Little Rock, lost the Black vote to Stevenson who had an open segregationist on his ticket, didn't he?  Nixon solidified Blacks not voting Republican.  He didn't even come close to starting the trend, and it's a historical fact that Blacks overwhelmingly backed a POTUS (FDR) who vetoed anti-lynching legislation and appointed a Klansman to the SCOTUS.  Anyone who says the Black vote left the GOP over anything other than economics is lying or an idiot.  It left "again" post-Nixon ... uh, so what?  It was never coming back.

I think a lot of the more affluent, middle-class black voters (such as those with longstanding roots in the North whose families had been Republicans since the Civil War) voted Republican up until the civil rights movement of the 1950s and 1960s. It was their significantly more numerous downscale counterparts - many of whom had recently moved into Northern cities from the South during the Great Migration, and who became part of the urbanized working class there - who started the big shift toward the Democratic Party.

The Southern Strategy and backlash/right-wing populism has made a difference in expanding the GOP's appeal to lower-middle and working class whites, but it has also made a difference in alienating a lot of voters (not just black ones) who might otherwise have voted Republican in the past.