Russia defends its enormous borders with the threat of nuclear war. It’s this threat that has long stopped Ukraine and its allies from attacking Russia on its home turf—there are ‘red lines’ that can’t be crossed without nuclear retaliation. Yet Ukraine just invaded Russian sovereign territory and still, no nukes. Volodymyr Zelenskyy appears to be calling Vladimir Putin’s bluff. It seems the ‘red lines’ were done in red pencil, not red pen. So how does this reshape the war, and what does it mean for Putin?