WASHINGTON — Nippon Steel and U.S. Steel are filing a federal lawsuit challenging the Biden administration’s decision to block a proposed nearly $15 billion deal for Nippon to acquire Pittsburgh-based U.S. Steel. The suit, filed Monday in the U.S. Court of Appeals for the District of Columbia, alleges that it was a political decision and violated the companies’ due process. “From the outset of the process, both Nippon Steel and U.