Sometime there are variables that are considered that are not obvious or public. I imagine the risk associated with a single source supplier is fairly large, and for the DoD keeping Northrup Grumman as major player in the game might sound appealing. Boeing is in the realm of large jets pretty much the only show left in town and if NG looses this deal they too fade from the picture. -IMHO
Another consideration is that ultimately airframes intended for the civilian domestic or international markets may be built there. Not only do you have the USAF being supplied, but possibly Australia and others. The US is a highly competitive location for production.
In the end, it's NG that is the system integrator and assembly will be in the US, many of the subcomponents on an Airbus even built in Europe are North American anyhow. The big gripe I would have had, is if this plane were built in Europe. I'm all for free trade, but national security/defense related industry should not be off-shored. Furthermore, those who over years have benefited from protectionism and subsidies keeping US goods and services off their market should not be rewarded with US tax money.
Not Australia, Delivery date of the final KC-30B on the order is next year. May be a chance on UK, Saudi, or UAE orders.
I thought Lockheed had the F22?