Georgia's sixth district is full of rich white Republicans. It went hard for Trump in November 2016. Handel pulled of a much more narrow win, and the Republicans spent a shit-ton of money to pull it off. The big story isn't that Republicans won a reliably Republican-leaning district -- it's that Republicans had to struggle to win their reliably Republican-leaning district.
Of course trolls who regurgitate everything Breitbart tells them think IT'S THE END OF TEH DEMONCRAP PARTY LOL LOSERS MAGA, because that's really their only strategy. Gloat, hate brown people, tell everyone History Has Ended and things will never change.
The Democrats have a lot of work to do, and plenty of it uphill. The Republicans, on the other hand, have branded themselves as the Party of Trump in a time when Trump is historically unpopular. That's going to lead to trouble down the road for Republicans.
Breitbart thinks their side has won permanently. If I may quote the eternally celebrated jasonm: "The end of self-doubt is the beginning of hubris."