They didn’t decide to switch sides, though you’re right in raising this issue. Instead they split in half. The Southern wing of the Democratic Party, the group that controlled the whole South where Republicans held almost no power and littler influence and where Nixon didn’t even appear on the South Carolina ballot in 1960, were the radical haters that revolted. They had an insurrection, which had been mounting for as decade, after the Brown v. Board decision. They threatened to basically secede from the Union if integration was forced by signing the Southern Manifesto. The first draft, that saw about 100 signatures of DEMOCRATIC Party Southerners, swore that they would NOT obey the Supreme Court ruling of Brown and integrate schools. Not Obeying the Supreme Court ruling is insurrectionist.
But it’s not surprise given that they didn’t bother obeying the constitution from all of the massacring and lynching done on black Americans from 1865-1965. How so? Because they refused due process rights on black Americans accused of crimes and instead lynched them. This was Solid South of the Democrats. Solid because the Democratic Party had a near absolute lock on power and kept black Americans out of politics, about 90-99 percent of the time—not allowing them justice or voting, basically denying them access to their Constitutional Rights. So when that great Traitor to their Southern Democrat way of life by signing the Civil Rights Act of 1964, they revolted and abandoned the party, going to the Republican Party, who they flirts with during the last FDR phase, having found a bit of common ground on the issue of cheap labor via their shared opposition to unions.
The Northern Democrats stood there, speechless, with the handful of black Democrats that had joined their party by chance but held no power. Once they lost the Southern Democrats to the Republican Party, they lost a sure path to the White House, as the 154 electoral Democratic Southern votes now swung to the Republicans. Nixon, who had worked on Civil Rights and helped in that regard pass the 1957 Civil Rights Act, the first one since the Civil War, though the rest of his party was tepidly for civil rights, had no choice but to embrace this new bigot wing of insurrectionist democrats that entered his Republican party if he wanted a chance at winning the election. It wasn’t a strategy as merely a lack of choice and courting them was they way to the White House.
While Reagan had been a racist Democrat and Governor who also defected from the Democrats to the Republican Party, was more ready to embrace the new Southern wing because of their shared white supremacist views. Like Trump, once a Democrat as well and whose father was a Klan member, Reagan actively promoted the welfare queen trope for years and years in the 1970s as a way to reinforce his supremacist brand the way Trump touted for years the “birther” theory for the same display of supremacy to the Southern voter, as a way to display allegiance to the Southern wing. Reagan wasn’t trying to “turn” the Southerners as much as he was signaling to the West coasters the new brand of Republican Party message that was moved to the core—white supremacy. Trump was doing this in the North and Rust belt. The wracked out Republicans we say today are really the same Southern wing of old. They bent the Democrat Party to their will by violence by 1901, and now they are bending the Republican Party to its will, wiping out the decency that once existed. They’ve never stopped being disloyal to the principles of due process and anti-federalism and inalienable rights represented by the constitution. It’s the rest of the country always making excuses for their perpetual insurrectionist behavior to that foundational democracy ideology of inalienable rights and equality and justice (due process), allowing them to be called American when they display the racism and misogyny and adherence to autocracy that is anything but.
