New U.S. intelligence assessments have reportedly warned that Vladimir Putin could test NATO’s resolve with a limited attack on an allied country as early as autumn 2026. The key question is whether NATO—and especially the United States—would respond decisively to a “sub‑Article 5” hybrid challenge aimed at dividing the alliance rather than defeating it outright. NATO says it remains ready to deter and defend, but the warning arrives as Russia modernises its military and the U.S. faces pressure on weapons inventories after the Iran war.