In the later 1960s, when the Republican Party capitalized on (and incensed) racist backlash to the Civil Rights Movements.

Rick Perlstein's books Before the Storm and Nixonland describe how in the 1950s and early 1960s, African Americans in the South were overwhelmingly supporters of the Republicans, yet in practice rarely could seriously participate in politics. African Americans in the North were typically the children or grandchildren of Black Republican migrants from southern states. These people arrived in northern cities with preexisting sympathies to the Republican Party, but were quickly courted by Northern Democratic political machines who sought to incorporate these new voters.

Due to the association of the Democratic Party with white supremacy in the South, many African American voters were initially hesitant to support the Democrats and remained Republicans. This made northern Black voters a very important swing constituency in the 1950s and early 1960s. But during and after the Civil Rights movement, Northern Democrats became more likely than northern Republicans to support the movement -- to the shock and horror of inveterate racists among the Southern Democrats.

As the Kennedy and particularly Johnson administrations began to embrace the Civil Rights Movement, leading to the passage of legislation the reenfranchised Black voters in the South, the Republican Party in the North increasingly embraced the kind of racist fear-mongering that was previously mostly associated with politics in the South. This led to a realignment during the Johnson and Nixon presidencies, in which Black voters largely abandoned the Republican Party and became Democrats nation-wide, and white voters in the South began to increasingly vote for a Republican Party that they had previously associated with the hated North and racial progressivism. Correspondingly, figures like Barry Goldwater and particularly Richard Nixon used racist feats of school and suburban integration to attract northern white voters, mostly of recent immigrant descent, into leaving the Democratic machines and voting for racist conservative Republicans.