Gerrymandering is a serious threat to the Democrats

"But whether Ossoff can pull off the improbable upset or not, Democrats will continue to face deep structural disadvantages to reclaiming Congress — most notably, gerrymandered congressional districts and the incumbency advantage that favors those running for reelection. 

Unless those change, Democrats will continue to face an uphill battle to winning back the House, even amid an extraordinary surge in grassroots activism among their base."