The ability to adapt to a constantly evolving security environment has been critical to the success of NATO, yet this is being tested anew as the Alliance faces a second term of Donald Trump in the White House and re-embraces collective defence in light of Russia’s war on Ukraine. Despite notable solidarity and unity in the immediate aftermath of the Russian invasion and significant progress in rebuilding the Alliance’s defence and deterrence architecture, the list of challenges facing the NATO Alliance is significant. This paper focuses on four of the most critical gaps: in the fields of command structure, military capabilities, force posture, and asymmetric defence. It also offers actionable recommendations for progress in advance of NATO’s Hague Summit in June 2025.