USG says 'it is impossible for us to cooperate with Russia'

The US government has contacted Turkey to say that if Turkey buys anti-aircraft systems from Russia the US will not sell Turkey any fighter planes, on the grounds that US government finds it literally physically impossible to imagine a world in which it refrains from antagonising Russia:
The Russian government has not issued a similar ultimatum and is understood to be accepting of a situation where Turkey buys military equipment from both Russia and the US.
Turkey has been given a deadline of the end of July to choose between buying US fighter jets and Russian anti-aircraft missile systems.
Acting US Defence Secretary Patrick Shanahan set out the ultimatum in a letter to his Turkish counterpart, Hulusi Akar.
Turkey, he said, could not have both America's F-35 advanced fighter jets and Russia's S-400 systems.
The Russian government has not issued a similar ultimatum and is understood to be accepting of a situation where Turkey buys military equipment from both Russia and the US.