But the race is also emblematic of each party’s current political messages. Jon Ossoff and the Rev. Raphael Warnock, the Democratic Senate candidates, have put forth an array of policy proposals that blend the shared priorities of the moderate center and the progressive left: passing a new Voting Rights Act, expanding Medicaid without backing a single payer system, investment in clean energy while stopping short of the Green New Deal, and criminal justice reform that does not include defunding the police.

Republicans are seeking no such calibration. Mr. Perdue, who announced on Thursday that he would quarantine after coming into contact with someone who had tested positive for the coronavirus, and Ms. Loeffler are banking that their loyalists are motivated more by what their candidates stand against than by what they stand for…

“The biggest factor for me is stopping socialism,” said Melinda Weeks, a 62-year-old voter who lives in Gwinnett County. “I don’t want to see our country become the Chinese Communist Party.”