Georgia's Dec. 6 runoff election pitting Democratic Sen. Raphael Warnock against Republican Herschel Walker is historic for having two Black candidates representing major parties on that state's ballot. But the voting law that mandated a runoff when neither candidate won a majority in November's election is actually a vestige of racist legislation.

Since the 1960s, Georgia's majority voting law has required a candidate get 50 percent of the vote or more in order to be declared the winner, and was introduced by a staunch segregationist legislator named Denmark Groover. Even now, the law "makes it more difficult for any group which forms a minority in the population to elect its candidates of choice," regardless of the candidates' ethnicity, historian and California Institute of Technology professor Morgan Kousser told the PBS NewsHour's Nicole Ellis.

Watch the conversation in the player above.

When so-called "white-only primary" elections were deemed unconstitutional in 1946, Black voter registration surged across the South, including in Georgia. In 1940, an estimated 250,000 Black southerners were registered to vote and that number rose to 775,000 by 1948, according to data from the National Park Service.

When Groover lost reelection to the Georgia House of Representatives in 1958 despite winning the majority of the white vote, data from segregated polling places in Macon revealed that Black voters contributed to the upset victory by his opponent, Kousser said. In his book, "Colorblind Injustice: Minority Voting Rights and the Undoing of the Second Reconstruction," Kousser writes that Groover's opponent "triumphed by garnering black ballots by a five-to-one margin."

As part of the civil rights movement of the 1960s, advocates, judges, and policymakers pressed for expanded and more equitable voting rights. Fear of losing white political supremacy prompted some white state and local legislators to move strategically to protect their racial agency in politics.

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When Groover won his seat back in 1963, he led the charge to break up what he described as the "Negro Voting Block," by transitioning Georgia from plurality voting, which allows the candidate with the most votes to be declared the winner, to majority voting - forcing voters to choose between the two candidates with the most votes in a separate runoff election. Kousser explains that majority voting may seem innocuous, but if the vote is racially polarized, "runoffs discriminate against Blacks because they are a minority of the voters."

Two decades after introducing majority vote legislation, Groover left very little to mystery to his motives, stating in a deposition, "I was a segregationist. I was a county unit man. But if you want to establish if I was racially prejudiced, I was. If you want to establish that some of my political activity was racially motivated, it was."

Groover's perspective later changed and he sought to amend segregationist policies he helped champion early on, but majority voting and its segregationist roots remain in place.

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According to Kousser, this legacy makes for a very tight race between Walker and Warnock. "Blacks are about 30 percent of the registered voters in Georgia and there is still quite racially polarized voting" in that state Kousser said.

In the Nov. 8 election, Warnock received 49.4 percent of the vote, while Walker received 48.5 percent - a tight contest where white and Black Georgians split on their preferred candidate. According to AP VoteCast data on the results of the November midterm election, 90 percent of African American or Black voters favored Warnock, while a majority of white voters -- 68 percent -- favored Walker. This coming Tuesday, the next senator from Georgia will likely be picked by whichever party turns out in greater numbers to vote.