【明報專訊】After Keith Krach, a US Under Secretary of State, visited Taiwan in mid-September, warplanes from the People's Liberation Army crossed the median line of the Taiwan Strait repeatedly for two weeks. The tones of US and Taiwanese high-ranking government officials have also changed. It can be seen that Beijing's declaration of its position has unveiled Washington's bottom line, i.e. its unwillingness to be mired in Taiwan Strait warfare.