In Georgia’s Senate runoff elections, Republicans are banking on a strategy that generations of segregationist politicians perfected: Array the voters in rural counties, overwhelmingly white and conservative, against those in the Atlanta area. From the Jim Crow era to our day, the antagonism between rural enclaves and greater Atlanta has shaped Georgia’s politics.

The Republican senators, David Perdue and Kelly Loeffler, have decided that the key is turning out their rural base. Yet the rapid growth of metropolitan Atlanta, combined with tireless efforts to protect African-Americans’ voting rights, has transformed the state’s political landscape.

Joe Biden’s victory in Georgia was especially meaningful not only because it upended decades-long trends in party politics but also because it represented a possible turning point in a much longer racial history. Mr. Biden is the first Democrat to carry Georgia since Bill Clinton in 1992. Mr. Clinton, though, won the state with only 43.5 percent of the vote, and he performed well among white voters in rural areas. Mr. Biden put together a very different political coalition — more urban and suburban, more multiracial and more progressive. It is this coalition that the Democratic Senate candidates, Jon Ossoff and the Rev. Raphael Warnock, are counting on.

Politicians in Jim Crow Georgia possessed a tool that Mr. Perdue and Ms. Loeffler would have envied: the county-unit system. The winner of each county received all of its unit votes. The eight largest counties had six unit votes apiece, 30 counties possessed four unit votes each, and the smallest 121 counties held two unit votes apiece. In 1950, Georgia’s three least-populous counties — with 9,267 total residents — combined for six unit votes, the same as Fulton County, with 473,572 residents. This system of malapportionment empowered demagogues, none more successful than Eugene Talmadge.

Wealthy executives bankrolled Talmadge’s numerous political campaigns, while many white farmers supplied the votes. (He served three terms as the state’s governor — two from 1933 to 1937 and one from 1941 to 1943.) Talmadge was a vocal opponent of the New Deal, yet he depended on the support of those impoverished Georgians who stood to benefit from many federal programs. The journalist Robert Sherrill, in his book “Gothic Politics in the Deep South,” explained why “the people” still stood by Talmadge: “Old Gene had never done anything for them, but he made them feel like people, fit for laughter, supreme over the black man at least, and sharing with him the sly knowledge that since only the rich could profit from government, the poor man was foolish to take government seriously.”

In many ways, Talmadge — though he was a Democrat and his party backed the social programs of the early New Deal — created a blueprint for today’s Republican Party. He combined racial animus with anti-government rhetoric, piled up votes among rural whites and exploited a system that gave those voters disproportionate power.

In the Georgia Senate races, the Republicans’ most insistent line of attack is that a Democratic-controlled Senate will lead America to socialism. Ms. Loeffler’s opponent, Mr. Warnock, would become Georgia’s first African-American senator. In one debate, Ms. Loeffler referred to “radical liberal Raphael Warnock” no fewer than 13 times. (Mr. Warnock responded that his economic philosophy derived from Matthew 25.) This is not so different from the way Talmadge raged against the New Deal as a socialist-inspired plot that would bring racial equality to Georgia.

Talmadge defended white supremacy and encouraged his supporters to use intimidation and violence to keep Black voters away from the polls. After losing a bid for re-election in 1942, he ran again for governor in 1946. He whipped white Georgians into a frenzy. Just before a Democratic primary in July, Talmadge told a crowd, “If I’m your governor, they won’t vote in our white primary.” In Butler, a veteran named Maceo Snipes cast his ballot in that primary election, becoming the first African-American to vote in Taylor County. The next day, four white men went to Snipes’s home and shot him. Snipes died days later.

Roughly 85,000 Black Georgians voted in that election, though tens of thousands were disenfranchised — by either voter purges or outright intimidation. An estimated 98 percent of African-Americans voted for Talmadge’s opponent James Carmichael, a businessman and more moderate Democrat. Carmichael won the popular vote by more than 16,000, but Talmadge won a solid majority of county-unit votes — and he thus won the primary election. (Talmadge also won the general election but died before his inauguration.)

As Jim Crow began to crumble in the 1960s, so did the county-unit system. The Supreme Court’s 1962 decision in Baker v. Carr established the principle of one person, one vote, and its 1963 ruling in Gray v. Sanders outlawed Georgia’s system.

The state’s politics have since been reshaped by demographic change. Democrats now perform poorly in white rural areas but rely on the expanding suburbs. Two counties tell this tale: Bacon County, in rural southeastern Georgia, and Cobb County, in suburban Atlanta. Bacon County was Talmadge country. In 1946, Talmadge defeated Carmichael by 1,317 votes to 277. Cobb County went strongly for Carmichael, and it formed part of the urban-suburban coalition that gave Carmichael a popular-vote victory.

In 2020, the old Talmadge strongholds were President Trump’s territory. He won Bacon County by a margin of more than 70 percentage points, but suburban areas like Cobb County powered Mr. Biden’s victory. Cobb was a Republican bastion from the 1960s through 2012, but in the past decade, the county has grown even more racially diverse and decidedly Democratic, supporting Mr. Biden by a margin of more than 14 points.

Mr. Biden won 30 counties in Georgia, and Trump won the other 129. Mr. Biden’s coalition encompassed the suburbs together with Atlanta, and Mr. Warnock and Mr. Ossoff are mobilizing voters in those places. Even if the architects of the county-unit system could not have fathomed the dramatic changes that have remade the Atlanta area, this was the kind of urban-suburban coalition that they feared. For those who believe the nation can achieve a multiracial democracy, the same coalition holds their most fervent hopes.

Jason Sokol (@jasokol) is a professor of history at the University of New Hampshire and the author of three books on the civil rights movement, including “The Heavens Might Crack: The Death and Legacy of Martin Luther King, Jr.”

The Times is committed to publishing a diversity of letters to the editor. We’d like to hear what you think about this or any of our articles. Here are some tips. And here’s our email: letters@nytimes.com.

Follow The New York Times Opinion section on Facebook, Twitter (@NYTopinion) and Instagram.