WASHINGTON — President Barack Obama faced deep resistance Thursday to plans for a possible military strike against Syria, with U.S. lawmakers demanding more proof that Bashar Assad's government perpetrated a deadly chemical weapons attack and Britain's Parliament rejecting military action in a stunning late night vote. Even so, the U.S. could launch action within days. Unless British Prime Minister David Cameron defies Parliament, Obama faces the prospect of proceeding without a major ally that was expected to come on board.