Tomorrow is the 20th anniversary of the bloody crackdown near Tiananmen Square, when Chinese troops gunned down unarmed civilians. No one knows how many died, and the government is still trying to prevent citizens from remembering what happened. Foreign journalists have been barred from the square, Internet sharing sites have been shut down and dissidents have been confined to their homes or required to leave Beijing. John Pomfret, former Beijing Bureau Chief for the Washington Post, is author of Chinese Lessons: Five Classmates and the Story of the New China.