For the first time, a ballistic missile launched by Yemen's Houthi rebels reached toward Riyadh, crossing a threshold that transforms a years-long regional conflict into something more intimate and more dangerous. The Saudi capital — seat of royal power, symbol of the kingdom's permanence — has long sat at a presumed safe distance from the war's reach, and that presumption now belongs to the past. What unfolds next will reveal whether this was a demonstration of capability or the opening note of a sustained campaign against the heart of Saudi Arabia.