What Bush did is inherent in his statement. If he did not agree with the communists that Taiwan Taiwan and specifically Chen Shui-bian were not engaging in behavior meriting attack then why did he make any statement at all?
Why has the president MOST supportive of Taiwan in recent memory given China the green light to attack Taiwan?
I don't know. He followed bad advice, clearly. This is an approach or policy that's been around a while now. It first cropped up during the Clinton administration. It was developed by a bi-partisan group, many at Kennedy School in concert with Beijing. Joseph Nye wrote the first op-eds about it in the late 90's. People in Bush's administration have always subscribed to it and have always pressures Bush on this.
Clinton's administration followed the same pattern, except he waited until his second term to do it.