Russian authorities said that a truck bomb on Saturday caused a fire and the collapse of a section of a bridge linking Russia-annexed Crimea with Russia — a key supply artery for Moscow’s faltering war effort in southern Ukraine. The attack on the bridge comes a day after Russian President Vladimir Putin turned 70, dealing him a humiliating blow that could lead him to up the ante in his war on Ukraine. Russia’s National Anti-Terrorism Committee said that the truck bomb caused seven railway cars carrying fuel to catch fire, resulting in a “partial collapse of two sections of the bridge.” The committee didn’t immediately apportion blame. The Crimean Peninsula holds symbolic value for Russia and is key to sustaining its military operations in the south. If the bridge is made inoperable, it would make it significantly more challenging to ferry supplies to the peninsula. […]