(There are some pundits who claim this is some secret they've uncovered, but it's long been front & center in any US history.)
President Woodrow Wilson, for instance, instituted segregation in Washington and across the federal government. (See @EricSYellin's work.)
When the second KKK rose to power in the 1920s, it had a strong Democratic ties in some states; strong GOP ones elsewhere.
See this thread:
Democrats still had a base of segregationists in the South, but increasingly some liberals in the North.
Republicans, liberal & even radical in Lincoln's era, had more conservatives joining, often in the West.
(Among dozens and dozens of great books on this, see Ira Katznelson's Fear Itself: nytimes.com/2013/04/07/boo…)
Though some in the administration (Eleanor Roosevelt, progressive Republican Harold Ickes, etc.) were racially liberal, the Democrats as a whole were not.
Blacks stayed loyal to "the party of Lincoln" in 1932, but shifted in massive numbers to FDR in 1936. (~76% of northern blacks)
This tension came to a head in the 1948 election, under the leadership of President Harry Truman.
Then -- to the nation's shock -- he pressed hard for all its recommendations, including protecting black voting rights and desegregating the military.
It was a turning point for the party, the first major fight on civil rights in which northern liberals beat back southern conservatives and took control of the party on race relations.
The Dixiecrats came back into the coalition, but increasingly saw that they were on the losing end of things.
Republican President Dwight Eisenhower and Illinois Gov. Adlai Stevenson, his Dem opponent in 1952 & 1956, both tried to duck the issue whenever possible.
After Brown v. Board, he said appointing Chief Justice Earl Warren had been "the biggest damfool mistake I ever made." He refused to urge compliance with Brown, allowing southern Democrats to wage "massive resistance" to it.
But until the Birmingham protests in 1963 he was generally reluctant to act, just as Ike had been.
He signed it into law in July 1964 with Martin Luther King at his side:
It *was* a Democratic admin's bill, but Southern Dems in the Senate blocked it at every turn, so Democratic leaders reached out to Minority Leader Everett Dirksen to get GOP votes to help pass it.
Personally, Goldwater wasn’t a bigot. He opposed not integration itself, but federal intervention to achieve it.
Goldwater carried four Deep South states that fall, with segregationists rallying to the GOP.
Importantly, he secured a rare deal with the GOP whereby he'd keep his seniority, and all the congressional power that came with it.
Until 1964, it seemed clear that Democrats were the party of economic liberalism and the GOP economic conservatism, but civil rights had been left out of the picture.
Asked which party was more likely to support school integration in 1964, 56% pointed to Democrats while 7% did so for the Republicans.
But, that said, there was *not* an immediate, massive change in party affiliations for elected officials in Washington. The "realignment" that scholars write about didn't happen overnight.
Most of the other old Dixiecrats in Congress didn't switch parties themselves, but oversaw a transition for the next generation.
When Colmer retired in 1972, he handpicked Lott to fill the seat -- but told him to run as a Republican. He did & won. nytimes.com/2002/12/15/us/…
When Helms ran on his own in 1972, though, like Lott, he ran as a Republican.
It didn't happen overnight, but stretched on until the 1990s in some places. But the trend was clear & well documented.
The authoritative study, though, remains the work of the political scientist twins Merle Black and Earl Black: amazon.com/Rise-Southern-…
That, however, is filled with factual errors and faulty premises. Here's a typical review from the Journal of Southern History
I'm not sure who this "Steve" is who's texting you, but he really doesn't know what the hell he's talking about.