The EU can ' t afford to kick the UK completely out , because the military defense of the EU rests heavily on NATO the UK ' s the secondbiggest military involved and # 3 ain ' t close . The idea that the UK will be happy to continue to commit to the defense of an EU that won ' t even deign to trade with it is a fantasy . Further , anything that affects the UK ' s participation in NATO is also likely to affect the US ' s commitment as well , especially since that ' s already on shaky ground , especially after Trump ' s election . The EU could possibly survive a UK withdrawal from NATO , but a US withdrawal would be a deathblow to the treaty . On top of that , proBritish sentiment in the US is fairly widespread , while proEU sentiment is much less so . The EU would be foolish to push the US into making a choice between the EU and the UK . Ultimately , the parties involved all know this what you ' re seeing is just the chestthumping before actual negotiations begin . But both parties need an agreement the UK for economic reasons , the EU for defense ones and neither party can afford to go fully to the mat to get its way .