CUSTER, S.D. — A silver minivan decorated with a large sticker reading “Love Your Neighbor Tour” recently circumnavigated South Dakota. Catholic nuns, Protestant pastors, a synagogue president, and a Muslim nonprofit professional were among the interfaith leaders who packed into the rented six-seater or caravanned behind. The road trip’s mission: to register voters and urge them to support expansion of the state’s Medicaid program to cover thousands more low-income adults. “If we are living our faith, then we have a serious obligation to love our neighbor and to show that in very practical way…