Their arrival marked the beginning of a tectonic shift in American political life. “The difference in laws between the North and the South created a political coming-of-age for Black migrants,” the political scientist Keneshia N. Grant writes in “The Great Migration and the Democratic Party: Black Voters and the Realignment of American Politics in the 20th Century.” “Seeing political participation as a badge of honor and hallmark of success in northern life, migrants registered to vote in large numbers. Northern parties and candidates worked to gain Black support through their election campaigns, and the parties expected Black voters to turn out to vote for their nominees on Election Day.”

For a Democratic Party whose national fortunes rested on control of urban machines, Black voters could mean the difference between four years in power and four years in the wilderness. With the rise of Franklin Roosevelt, who won an appreciable share of the Black vote in the 1932 presidential election, Northern Democratic politicians began to pay real attention to the interests of Black Americans in cities across the region.

By 1948, most Black Americans who could vote were reliable partners in the New Deal coalition, which gave liberals in the Democratic Party some of the political space they needed to buck Jim Crow. Yes, the Dixiecrats would withdraw their support. But for every white vote Harry Truman might lose in Alabama and Mississippi, there was a Black vote he might gain in Ohio and California, the two states that ultimately gave him his victory over the fearsome former prosecutor (and New York governor) Thomas Dewey.

Not only did the Dixiecrat rebellion fail, it demonstrated without the shadow of a doubt that Democrats could win national elections without the Solid South. The segregationists were weaker than they looked, and over the next 20 years the Democratic Party would cast them aside. (And even then, with the Dixiecrat exodus, Truman still won most of the states of the former Confederacy.)

There is no equivalent to northern Black voters in the Trumpified Republican Party. Put differently, there is no large and pivotal group of Republicans who can exert cross-pressure on MAGA voters. Instead, the further the Republican Party goes down the rabbit hole of “stop the steal” and other conspiracy theories, the more it loses voters who could serve apply that pressure.

In a normal, more majoritarian political system, this dynamic would eventually fix the issue of the MAGA Republican Party. Parties want to win, and they will almost always shift gears when it’s clear they can’t with their existing platform, positions and leadership.