Under one view, credibility is like a chain. If the United States does not keep one of its public promises, the credibility of the chain falls apart. In essence observers are using the behavior of the American government to draw inferences about its true underlying type. A single act of breaking a promise or failing to honor a commitment would show we really cannot be trusted, or that we are weak and craven, and so that characterization of our true type would be applied more generally to all or most of our commitments.
Under a second view, we don’t have that much credibility in the first place. To be sure, we can be trusted to do what is in our self-interest. But there is not much underlying uncertainty about our true type. So we can promise Ruritania the moon, and fail to deliver it, and still the world thinks we would defend Canada if we had to, simply because such a course of action makes sense for us. In this setting, our violation of a single promise changes estimates of our true scope of concern, but it does not much change anyone’s estimate of the true type of the American government.
Insofar as you believe in the first view, our inability/unwillingness to honor our commitment to the territorial integrity of Ukraine is a disaster. Insofar as you hold the second view, our other commitments remain mostly credible.
For the most part, I see the second view as more relevant to understanding U.S. foreign policy than the first. We’ve broken promises and commitments for centuries, and yet still we have some underlying credibility. Remember those helicopters evacuating Saigon rooftops in 1975?
Still, when it comes to Taiwan, or those Japanese islands, or other Pacific islands, I think the first view plays a role. That is, I think the world does not know our true type. How much are we willing to risk conflict to limit Chinese influence in the Pacific? Whatever you think should be the case, what is the case is not clear, perhaps not clear even to our policymakers themselves. (In contrast there are plenty of data on the parameters of American preferences toward Middle East and Israel-linked outcomes, and our willingness to incur costs to alter those outcomes.)
That is another way of thinking about why the Ukraine crisis is scary for the Pacific. It is one reason why the Nikkei was down 2.5% shortly after market opening Monday morning (Asia time) and ended up 1.3% down for the day. The Chinese stock market did just fine.