This article examines the Green Party of England and Wales' evolving and increasingly contested position on NATO membership between 2023 and 2025. Drawing on conference debates, parliamentary statements, leadership rhetoric, and internal party documents, this analysis reveals a fundamental policy crisis emerging from irreconcilable contradictions between pacifist ideology and security pragmatism. The 2023 conference decision to abandon the party's historical opposition to NATO—driven by Russia's invasion of Ukraine—has triggered a significant grassroots backlash, intensified by Donald Trump's return to the US presidency. This study documents how external geopolitical pressures, particularly Trump's destabilization of transatlantic relations, have catalyzed internal party conflict, positioning NATO policy as a defining ideological battleground. The analysis demonstrates that the current compromise position is functionally untenable, with the party's new leadership under Zack Polanski actively working to reverse the 2023 decision while managing electoral and strategic considerations.