The moral and ethical scale of the issue makes this far different than someone buying a pen.
If Lockheed could brick its planes if the US planned to use them for military action it disagreed with (and showed some indication they couldn't be trusted not to do it), would they be a supply chain risk?
It is not the role of a defense contractors to have oversight and control power over the military they're supplying.
Purposes Anthropic already spelled out in contract form.
They don’t buy the product, and the product can’t be used in the things they do buy.
Anthropic isn’t a supply chain risk since they easy found someone else