The Democrats’ one best hope at a competitive Senate race in Georgia is already exhibiting signs of weakness. Since her July announcement, Michelle Nunn’s nascent campaign has sought branding grounded in entrenched Georgia political roots, thanks to her famous father, while ensuring daylight between party and president. The Points of Light CEO made no mention of party affiliation in a campaign announcement email, and a two-week tour across the state, dubbed “What Washington Can Learn From Georgia,” appeared more akin to her career in nonprofits than a show of political force. Yet an increasing slew of unforced errors is undermining...