As US lawmakers return from their Easter break, they need to take Volodymyr Zelensky’s warning Sunday seriously: Without US military aid, Ukraine “will lose the war.” And if that happens, “other countries will be attacked.” Yes, it’s that simple. Ukraine’s military has been short of ammo and struggling to hold back Russia for weeks. Moscow is reportedly probing for weaknesses and planning new offensives to capture more Ukrainian territory. If US help fails to arrive, it’s just a matter of time before Zelensky & Co. are annihilated or forced to surrender. And anyone who thinks that outcome won’t endanger the...