The small trove of memorabilia are the centerpiece of the “June 4 Memorial Exhibit,” now housed on the fourth floor of a Manhattan office building. It carries on the mission of a similar exhibit in Hong Kong shuttered by the communist government two years ago. In recent years, China’s Communist Party has become more aggressive in squelching dissent and its attempt to erase any reminders of those heady days when tens of thousands of students challenged its power at Tiananmen. Fangsuo Zhou, now in his 50s, remembers all too well that dispiriting spring day in 1989 when tanks rolled into Beijing's Tiananmen Square. Communist troops swarmed in and the clubbing began — scores of pro-democracy university students were beaten and bloodied during the confrontation.