U.S. Secretary of State Marco Rubio jets to Brussels this week, stepping into a lion’s den of alarmed NATO allies rattled by the Trump administration’s cozy overtures to Russia and sharp jabs at transatlantic partners.

Arriving Thursday for two days of talks, Rubio faces a daunting task: soothing fears as President Donald Trump’s rhetoric—dismissing Ukraine’s NATO path and musing about annexing Canada and Greenland—threatens to unravel 75 years of American-led unity.

Europeans are jittery. Trump’s attacks on Canada and Denmark, coupled with his complaints about NATO spending, signal a potential U.S. retreat from the alliance’s mutual defense pact. With Russia’s war in Ukraine raging, allies crave clarity on Washington’s intentions—especially as Defence Secretary Pete Hegseth hints at shifting focus to Asia and U.S. borders. Could the 100,000 U.S. troops in Europe, including 20,000 sent post-2022, soon pack up?

Rubio, seen as a pragmatic voice, must navigate this storm. Allies want a roadmap—will U.S. nuclear might and the 6th Fleet stay put? NATO’s deterrence hinges on it. Yet Trump’s warmth toward Vladimir Putin muddies the waters, leaving diplomats asking: if Russia’s no threat, why hike budgets to 3% by June’s summit? “Rubio’s in a bind,” notes Jeff Rathke of Johns Hopkins. “Trump’s selling a Russian realignment while pushing allies to spend more against… Russia?” Europe braces for answers—and a possible reckoning.