One historical precedent was the Lend-lease act.

>In December 1940, Roosevelt introduced a new policy initiative whereby the United States would lend, rather than sell, military supplies to Great Britain for use in the fight against Germany. Payment for the supplies would be deferred, and could come in any form Roosevelt deemed satisfactory.

Basically we are just a material supplier. As long as we don't actually use our own troops to fight, we are not really "in the war". We are no different that those many other countries that supply medicine, fuel, food and other supplies.