The district has moved towards the Democrats in the last decade, but it should still be a solidly Republican district. In 2012, Mitt Romney overwhelmingly won it. Republicans running statewide have won it easily. Congressman Price won it easily. The only Republican who has had trouble winning it is Donald Trump. But that has made it hard for Karen Handel to win it.
Both sides have something to worry about in this too close to call race.
For the Republicans, they need to worry that they may be losing a solidly Republican district because 15% of the GOP is voting Democrat not to protest Karen Handel, but to protest President Trump. A number of Republicans, particularly Republican women, are using this vote as a way to voice their displeasure with President Trump, even if it means handing the seat to the Democrats.
With the GOP House majority at only a couple dozen strong, losing a seat like this is a big red flag for 2018.
For the Democrats, they need to worry that this race is so close despite spending upwards of $20 million with 15% of the GOP voting Ossoff. This is the sort of district they must win to take back the House, but they cannot do that if they have to spend that much money to be competitive. To be sure, an off year election requires more money and a greater focus of resources. But even with a GOP protest vote and an extended voter registration period to draw in new Democrat voters, the race is still very close. The Democrats had a fundraising advantage, media advantage, advertising advantage, off year advantage, etc. and their candidate has had to run like a moderate Republican who refuses to trash the President to get elected.
If the party is moving left, having people like Ossoff get elected who cannot move as left as his heart and his party would want is not good news for the Democrats. It opens them up to major primary fights later when Ossoff refuses to vote for things like a living wage or government funded healthcare in order to keep his position. We should not forget that Nancy Pelosi is as unpopular in this district as Donald Trump. Ossoff voting for Pelosi for Speaker would be used against him effective if he is able to pull this off.