By FATIMA HUSSEIN, JOSH BOAK and MARC LEVY WASHINGTON — President Joe Biden has blocked the nearly $15 billion proposed deal for Nippon Steel of Japan to purchase Pittsburgh-based U.S. Steel — affirming his earlier vow on the presidential campaign trail to prevent the acquisition of Steeltown USA’s most storied steel company. The proposed deal kicked up an election year political maelstrom across America’s industrial heartland and blocking it drew a threat of litigation from Nippon Steel. “We need major U.S.