Gentlemen,
As a USAF pilot who refuels evry month for actual missions and currency, there are alot of factors that go into this decision, many of which are far more complicated than “political” arguments.
For example the A-330 is deemed by many to be too large, also I have heard something along the lines that the wing loading is such that it causes much more turbulance to the tanking aircraft, also another argument concerning “wing-bending” issues. I’m not an engineer so please feel free to correct me. I do know the USAF is buying some 767’s and fleet commonality with NATO will be a big factor. Don’t view this as another instance of US forceing EU to buy American products, there are some serious limitations concerning the 330 airframe that make it less desireable for refueling purposes. I think the better option is maybe an A-300 version, but it wouldn’t have the range needed.