In light of the Cultural Revolution's horrors, Nixon's meeting with Mao appeared inexcusable -- and yet it surely helped set China on a path where millions of its citizens have been lifted from poverty and connected to open societies. Pope John Paul's engagement with Poland created space not just for the Catholic Church, but for labor leaders like Lech Walesa. Ronald Reagan's efforts on arms control and embrace of perestroika not only improved relations with the Soviet Union, but empowered dissidents throughout Eastern Europe. There's no simple formula here. But we must try as best we can to balance isolation and engagement, pressure and incentives, so that human rights and dignity are advanced over time.