Mr. Warnock narrowly defeated Mr. Walker on Tuesday. But Gov. Brian Kemp, a Republican, handily toppled Stacey Abrams, a Democratic star, in his re-election bid last month.
Only Pennsylvania and Michigan had clean Democratic sweeps in statewide offices.
Republicans, meanwhile, swept Florida, with Gov. Ron DeSantis winning re-election in the state by easily the largest margin by a Republican candidate for governor in modern history. In Ohio, Representative Tim Ryan, widely considered to be one the Democratic Party’s strongest candidates, lost his bid for Senate by six percentage points.
That new map isn’t entirely new, of course. Since 2008, Democrats have hoped that demographic changes and millions of dollars could help put the growing pockets of the South and West in play, allowing the party to stop chasing the votes of white, working-class voters across Ohio and Iowa.
But the party has made inroads before, only to backslide later. When Barack Obama carried North Carolina in 2008, pundits and party officials heralded the arrival of the Democratic revival in the New South. President Obama lost the state four years later and Mr. Biden was defeated there by a little more than a percentage point.
Democrats argue their victories in Georgia will be more resilient. Mr. Warnock’s coalition looked very similar to Mr. Biden’s — an alliance of voters of color, younger voters and college-educated suburbanites.
For Republicans, the winning formula requires maintaining their sizable advantage among rural voters and working-class, white voters, without fully embracing the far-right stances and combative politics of Mr. Trump that could hurt their standing with more moderate swing voters. Mr. Kemp followed that path to an eight-percentage-point victory.
But Mr. Walker was in no position to expand his voting base. He was recruited to run by Mr. Trump, despite allegations of domestic abuse, no political experience and few clear policy positions, and spent much of his campaign focused on his party’s most reliable voters.