Open this photo in gallery: An Israeli army transports a 155mm artillery shell near a self-propelled howitzer deployed at a position near the border with Lebanon in the upper Galilee region of northern Israel on Oct. 18.JALAA MAREY/AFP/Getty Images Joe Biden, in the first visit by a U.S. President to Israel in a time of war, has thrown his weight behind the Israeli government in its fierce battle with the Hamas militant group. But it remains unclear whether Mr. Biden’s efforts to ensure humanitarian aid enters Gaza will be successful. Thousands of tonnes of emergency relief supplies have been piled...