President Trump might have shocked some European leaders but the writing has been on the wall for decades: European states will have to take responsibility for their own security. Despite Russian aggression in Europe since Georgia (2008), and the promises made by NATO states in Wales 2014, there are only a few NATO states that can provide a degree of credible assurance on national security to their populations as the US withdraws. RUSI's Ed Arnold delves into the implications for national and regional security for individual states and multilateral bodies: from leadership and the consequences for NATO, to EU and EC funding mechanisms. Critically, the timeline for US withdrawal and European rearmament might not align: the resulting window when Russia could unpick the credibility of NATO arrives rapidly.