For all the hype about “Purple Texas,” the real front in the Democratic demographic offensive is Georgia.

No other plausibly competitive state has seen a more favorable shift for Democrats in the racial composition of eligible voters over the last decade. The pace of demographic change is so fast that Michelle Nunn, a Democrat, is locked in a tight race against the Republican David Perdue for an open Senate seat — even with an off-year electorate that is favorable for the G.O.P.

The pace of demographic change might even be fast enough to outpace the polls.

Polls show Mr. Perdue leading Ms. Nunn by about three percentage points. The various Senate models, including The Upshot’s, give Ms. Nunn about as good a shot — roughly 20 percent — of winning as Democratic incumbents in Louisiana, Arkansas and Alaska. But there’s reason to wonder whether her chances are better still: Recent polls are most likely underestimating the share of voters who are black, along with Ms. Nunn’s share of the vote.