WASHINGTON (Reuters) - The White House is drafting a backup immigration reform plan in case a bipartisan congressional committee working on a bill fails, an Obama Administration official said on Sunday, though a key Republican said the president's plan would be "dead on arrival" on Capitol Hill. White House Chief of staff Denis McDonough said the administration hoped that bipartisan efforts would deliver a broadly acceptable package, but wanted a plan B. "We're doing exactly what the president said we would do last month ... which is we're preparing. ...