US President Joe Biden branded Vladimir Putin a “war criminal” Wednesday as the Russian leader’s onslaught in Ukraine claimed more civilian lives, and a theatre where “hundreds” were sheltering was destroyed by bombing. Biden’s rebuke — his sharpest yet — came after Ukraine’s leader Volodymyr Zelensky made a searing appeal for help to the US Congress and the president himself, who responded by pledging $1 billion in new weapons to fight Russia’s invading army. Officials in the port city of Mariupol were struggling to count the dead at the Drama Theatre, where thick smoke rose from the rubble…