These Georgia Precincts Were Red. Then Blue. Now They Are Purple.

The Georgia voters who delivered Mr. Kemp a comfortable victory over his Democratic challenger, Stacey Abrams, in November did not show the same enthusiasm for Mr. Walker. Neither Mr. Walker nor Mr. Warnock cleared the 50 percent threshold needed to win outright, sending voters to the polls again for a runoff on Tuesday.

Mr. Walker received fewer votes than Mr. Kemp in nearly every precinct, including deep red areas in the north and Democratic areas along Georgia’s Black Belt, and fell short the most in the high-income suburban precincts of northern Atlanta. In total, Mr. Walker received 200,000 fewer votes, and the disparity was greatest in Atlanta’s metro area. If Mr. Walker had received just a third of these votes, he would have won the election.

These areas, home to a wealthy, highly educated and historically Republican electorate, have helped turn Georgia into a swing state.

Crossover precincts in the Atlanta suburbs — along with the area as a whole — have been shifting Democratic in recent election cycles. In 2016, these precincts voted for Mr. Trump by an average margin of nearly nine percentage points. In 2020, they supported Mr. Biden by six percentage points.

Several forces have shaped the evolving political bend and the apparent high concentration of ticket-splitters in Atlanta’s northern suburbs.

One is Mr. Walker’s scandal-plagued history, which has been a sticking point for many people who normally vote Republican. His campaign was dogged by his ex-wife’s allegations of domestic violence, the revelations that he had multiple children outside his marriage and that he paid for two women to have abortions despite maintaining a staunchly anti-abortion stance on the campaign trail.

“I think Herschel Walker may have been one of the very few people in the state who could be nominated by Republicans for the U.S. Senate and not win,” said Charles Bullock, a political science professor at the University of Georgia.

Mr. Walker lagged behind not only Mr. Kemp, but also the Republican candidates in every statewide race.

“I had no choice,” said Eric Franklin, a 51-year-old voter in Snellville, Ga., who said he voted Republican down the ballot with the exception of the Senate race, in which he opted for Mr. Warnock.

Mr. Franklin said he voted for Mr. Warnock not because he’s the best, “But he’s the best candidate to be in there right now.” He added: “It’s like you had to go with what you can deal with.”

The reasons Mr. Franklin gave for why even he, a self-described lifelong Republican, could not support Mr. Walker mostly related to the candidate’s character.

“Things here in Georgia will go totally south if he gets in there,” he said.

Another factor that led to ticket-splitting may be demographic change. Northern Atlanta’s once predominantly white suburbs have rapidly diversified as their populations have grown.

Two out of every five Atlanta-area crossover precincts are in Gwinnett and Cobb Counties, which are the most diverse in the state and home to fast-growing Black and Asian American populations. Both counties voted for Mitt Romney in 2012 and flipped to Hillary Clinton in 2016, the first time they had selected a Democratic candidate for president since 1976.

Mr. Trump has also played a role in shaping the state’s politics. Mr. Kemp, who as governor refused to help overturn the 2020 election results in Georgia, saw strong support in the state despite Mr. Trump’s ire, and he fended off a Trump-backed challenger in the primary. The outcome of Tuesday’s runoff with Mr. Walker, who was pressed to run by Mr. Trump, will shed more light on Mr. Trump’s influence in Georgia.

In November, given the choice between Mr. Walker and a Democrat for Senate, many Kemp voters decided to go with Mr. Warnock, the Democrat.

Some Kemp supporters did not fully cross party lines; they simply left the Senate space blank.

Richard Reilly, a 51-year-old Cobb County resident, said he supported the entire Republican ticket but declined to vote in the Senate race.

“I’m not excited about Warnock,” he said. “I mean, I’m tired of Democratic, you know, pork fat.” He described Mr. Walker as “a fine athlete,” but added: “I just, you know, I don’t know what kind of politician he’ll be. I mean, that’s the honest truth.”

Mr. Reilly, who voted for Mr. Trump in 2020, said he had not yet decided whether he would vote in the runoff election.

Overall, fewer people voted in the Senate election than in the governor’s race. But only a few precincts recorded significantly lower vote totals between the two races, suggesting that Mr. Walker’s underperformance was not primarily due to Kemp voters’ sitting the Senate race out.

Some Kemp supporters could also have voted for the Libertarian candidate, Chase Oliver. If Mr. Walker had received the entire Libertarian vote, about 81,000, he would have won outright (the same could be said for Mr. Warnock).

Dr. Bullock, the University of Georgia professor, estimates that a third of that 81,000, or roughly the number of people who voted Libertarian in the governor’s race, came from “true blue” Libertarians.

“I think the other two-thirds of the Libertarian vote were Republicans who couldn’t bring themselves to vote for Walker, but on the other hand would not vote for a Democrat,” he said. “And so this was a place where they could park their vote.”

It’s hard to say whether these Republicans will be motivated to turn out for the runoff, particularly as Senate control is no longer in play.

“To the extent that that is how a person felt and that’s why they voted for a Libertarian, I think there’s a good chance that they sit this election out,” Dr. Bullock said.

In the lead-up to the runoff, both Senate candidates have tried to make inroads with ticket-splitters.

Mr. Walker has spent more time campaigning in Atlanta’s suburbs and has embraced Mr. Kemp as a surrogate. The two Republicans campaigned together for the first time at an event in Cobb County in mid-November. Notably, Mr. Trump will not be campaigning in person for Mr. Walker.

Mr. Warnock has sought to portray Mr. Walker as unfit for office and as an ally of Mr. Trump. In one Warnock ad, a woman says she was “proud” to support Mr. Kemp in November but decided to back Mr. Warnock for Senate.

There have been only a few polls of the runoff, given the difficulty of estimating turnout, but they place the race within the margin of error.

“From looking at what’s happened so far this year, I would say that Georgia is not as blue as Democrats thought it was or hoped that it was,” said Dr. Bullock, pointing to Mr. Kemp’s strong showing in the general election compared with Mr. Trump’s in 2020, Mr. Kemp’s margin of victory in 2018 and the fact that Democrats made only modest gains in the state legislature.

But, he added, “Georgia is not as red today as it would have been 10 years ago.”