Even as the networks declared Mr. Obama the winner, Mr. Romney, who had earlier told reporters he had written only a victory speech, paused before the walk downstairs from his hotel room in Boston. It was 11:30 p.m., and Romney field teams in Ohio, Virginia and Florida called in, saying the race was too close for the candidate to give up. At least four planes were ready to go, and aides had bags packed for recount battles in narrowly divided states. Bob White, a close Romney friend and adviser, was prepared to tell the waiting crowd that Mr. Romney would not yet concede.