Since 2009, the Georgia Tea Party has held biweekly meetings in Cobb County, an affluent Atlanta suburb that has voted Republican in nine of the past ten national elections. One winter night, the group invited an unlikely guest speaker, a young activist named Marc Hyden. He came to give a presentation against capital punishment, a policy most in attendance endorsed. “Nearly all of us are what you might call traditional conservatives on this issue,” Steve Covert, a member of the advisory board, said. “We just believe that the death penalty is justified if someone is convicted of premeditated murder.…