It makes no sense for him to not consider the US because that would defeat the purpose of NATO.

The US has already breached articles 1 and 2, and made it clear they were ready to attack a NATO ally.

1. The Parties undertake, as set forth in the Charter of the United Nations, to settle any international dispute in which they may be involved by peaceful means in such a manner that international peace and security and justice are not endangered, and to refrain in their international relations from the threat or use of force in any manner inconsistent with the purposes of the United Nations.
2. The Parties will contribute toward the further development of peaceful and friendly international relations by strengthening their free institutions, by bringing about a better understanding of the principles upon which these institutions are founded, and by promoting conditions of stability and well-being. They will seek to eliminate conflict in their international economic policies and will encourage economic collaboration between any or all of them.

So it makes a lot of sense to consider how NATO would defend itself not only against the US but also in their absence in case of a conflict.