WASHINGTON (Reuters) - President Barack Obama is likely to delay the start of his Christmas vacation to help several of his key legislative goals pass Congress before the end of the year, the White House said on Monday. Obama is tentatively scheduled to depart on Saturday for Hawaii, where the family traditionally spends its year-end vacation. But lawmakers are still debating the extension of Bush-era tax cuts and a new nuclear weapons deal, both of which Obama is eager to see approved. "The president will be here for as long as Congress is here," said White House spokesman Robert Gibbs,...