Until the 1970s, Georgia was virtually a one-party state, with conservative Democrats dominant. But as conservative voters moved en masse to the Republican Party, Democrats were left concentrated in places like the city of Atlanta, adjacent and urbane Decatur, and smaller cities with significant African-American populations.
In the last few years, however, distaste for Trumpism has spread and demographic change has exploded, giving Democrats surprising new strength in the populous, vote-rich northern suburbs of Atlanta — places like Cobb and Gwinnett Counties that were once bastions of Republican power.
Hillary Clinton carried Cobb and Gwinnett Counties even as she lost the state in 2016. This year, Mr. Biden won them again. And he added to her margin in the state, significantly increasing the number of voters who voted Democratic in the counties that are home to Georgia’s most important second-tier cities — Augusta, Columbus, Macon, Savannah and Athens.
In recent months, the pandemic has slowed the Georgia economy, with unemployment rising to 6.4 percent in September from 5.7 percent in August. Covid-19 cases are increasing too; over the past week, there have been an average of 2,242 new cases per day, an increase of 42 percent from the average two weeks earlier.
A new generation of Democratic candidates has left behind the fiscal and social conservatism of its forefathers to embrace a rising demographic coalition of Black voters, college-educated suburban women and a more politically engaged younger generation.
Even if Mr. Biden’s victory was ultimately delivered by Northern industrial states like Pennsylvania, his slim margin in Georgia most likely points to the future of the Democratic Party, a future which come into clearer view in the Senate runoffs.
Republicans will try to stop any Democratic momentum, hoping to show that Mr. Biden’s strong performance here is more about Mr. Trump’s divisive candidacy than the G.O.P.’s loosening grip on the dynamic South. For Democrats, winning both seats would leave the parties at a 50-50 split in the Senate, with the vice president, Kamala Harris, casting the tiebreaking vote.