Mira Rapp-Hooper criticizes the idea that Crimean annexation has damaging implications for U.S. security commitments elsewhere:

According to this narrative, Washington’s failure to uphold the 1994 Budapest Memorandum portends U.S. complacency if Japan faces an attack in the East China Sea. It is tempting to attribute this to an acute case of “resolve anxiety,” but it is also important to parse why the failure of one international agreement does not imply the frailty of them all. If the United States is to remain powerful and engaged in the world at a time of great resource constraints, it will need to choose its battles wisely. This, in turn, requires that we acknowledge that not all international commitments are created equal [bold mine-DL].

In this case, Rapp-Hooper is comparing the Budapest Memorandum with the U.S.-Japan mutual defense treaty. As she notes, the former has no enforcement mechanism, and doesn’t really require its signatories to do very much at all. U.S. security guarantees to Japan, on the other hand, are part of a formal, ratified treaty that obliges the U.S. to defend Japan if it is attacked. Just as U.S. commitments to its treaty allies haven’t been undermined by the “failure” to attack Syria, they haven’t been jeopardized by the Ukraine crisis, either. These other cases tell us nothing about U.S. willingness to defend its allies, and it is extremely misleading to argue that formal commitments to allies are somehow on the same level as non-binding agreements or vague presidential threats.

Rapp-Hooper continues with a discussion of credibility:

Scholarly work suggests that states assess their opponents’ interests and capabilities with respect to the particular object under dispute, as opposed to their diffuse reputations for resolve towards all commitments in all cases. Nonetheless, credibility is necessarily perceptual and difficult to measure, and we do not have a firm understanding of whether and how it transfers across domains. It is, therefore, helpful to return to the formal definition of credibility itself: do the actors involved have the incentive to behave as they say they will? The Budapest Memorandum and U.S.–Japan guarantee could not look more different where incentives are concerned [bold mine-DL].

As she goes on to say, the U.S. can’t afford to treat every pledge as if it were the same as the commitments made to treaty allies:

But if the United States is to retain the resources to guarantee the security of thirty countries worldwide, it will not be able to make the same promises to states that do not hold those commitments.

These are the commitments that matter most, and they are the ones that the U.S. is truly expected to honor, which means that it will have to put them first and not exhaust itself by trying to back up every small pledge that it may have made over the years.