It is provocative, but not entirely inaccurate, to suggest that U.S. foreign policy these past few months has been sufficiently erratic to make America's allies reconsider the degree to which we can be trusted—and our adversaries re-evaluate the degree to which we must be feared.

The canary in the coal mine on such matters is Israel. None of America's allies is more sensitive to even the most subtle changes in the international environment, or more conscious of the slightest...