On Friday evening, Karen Giorno, a former senior adviser on Donald Trump’s presidential campaign, addressed a few dozen volunteers for Bob Gray, one of 18 candidates running for Congress in a special election this week in Georgia’s 6th District. The seat, which once belonged to Newt Gingrich, was supposed to be safely Republican. Former Rep. Tom Price, who stepped aside to become Trump’s secretary of health and human services, won November’s election by 23 points.