Luke Bretherton is new to Duke from England. A professor of ethics in Duke's Divinity School, he writes on a contentious topic -- how Christians should engage in politics. "Politics without piety is pitiless; piety without politics is pitiful," he writes in his latest book "Christianity & Contemporary Politics." In this "Office Hours" interview, he identifies key Christian voices on politics, describes virtues of the Southern Populist Movement, and lists strengths and weaknesses of the two American political parties. Read his blog at http://christianitycontemporarypolitics.blogspot.com. Follow him on Twitter @WestLondonMan.