For better or worse, building commercial aircraft from the size of a 737 and larger has become a world wide duopoly. There really is only room for two manufacturers. If Boeing only had domestic US content in its planes, they would be ceding much of the international market for their aircraft to Airbus, because Airbus would make sure parts from countries of potential customers would be in their planes. Boeing is using Russian engineers to develop the 747-400LCF freighter that will be used to transport components built by various suppliers to Boeing's factory near Seattle. Boeing is also buying lots of Russian titanium that will be used for the rings that hold the sections of composite fuselage together.
A friend of mine in Calif. is leasing part of his building to a company that is streatch forming skin parts for Airbust.
It's not just a one way street.