NATO summits are usually highly organized events. Heads of State and Government adopt previously negotiated decisions and define work plans up to the next summit. Above all, they aim to demonstrate unity and solidarity so that friend and foe alike believe that the NATO allies will defend each other in the event of a crisis. But this summit threatens to disrupt this process, because no one knows how US President Trump will behave. Will we see a revival of a brash Mr. Trump G7 Summit when the US President retrospectively ‘unsigned’ the communiqué via tweet? Or will he act as a patriarch, whose stubborn grumblings are ultimately met with cooperation, and keep the family bound together?