Chen is pushing the envelope and forcing the United States to draw a line to show him where the limit is.

It's not in the U.S. interest to push Chen into a corner.

The United States wants a manageable status quo. It doesn't want to see things out of control.

China has to calculate how to respond to not annoy the (Taiwan) populace and not fall into Chen's trap. Chen wants a strong reaction from China. They are watching what the United States does next, what the opposition parties do next, and then they will decide what to do.