As President Bush arrives in Shanghai for the Asia-Pacific Economic Cooperation summit, where he will meet with China’s president Jiang Zemin, FRONTLINE and The New York Times join forces to explore the U.S.-China relationship. As much as trade or the need for cooperation in the fight against terrorism, it is the flashpoint issue of Taiwan — the capitalist and now democratic island that China has been trying to reclaim for five decades — that remains the greatest source of tension between the world’s most powerful country and its most populous one.