Donald Trump's return to the White House in 2025 has shaken up transatlantic security once more. NATO has been the main part of European defence for decades, with the US providing important guarantees. Trump's renewed focus on his "America First" doctrine, which treats alliances as business contracts instead of long-term partnerships, makes people question what Washington has promised. His second term forces the EU to face an important question: can it protect its own safety if U.S. leadership is weak?