On a Saturday morning in late January, Russ Feingold descended a tight path in the hilly forests of the Democratic Republic of the Congo’s Kahuzi-Biega National Park to look for gorillas. The former Democratic senator from Wisconsin wore a long-sleeved safari shirt over a blue polo, a coiled bracelet to repel mosquitos, a surgical mask to protect the gorillas from human germs and two pairs of socks, with his zip-off cargo pants tucked into the outer pair to keep out ants.