WASHINGTON (AP) - Democratic Sen. Joe Manchin said Sunday he cannot back his party’s signature $2 trillion social and environment bill, dealing a potentially fatal blow to President Joe Biden’s leading domestic initiative heading into an election year when Democrats’ narrow hold on Congress was already in peril.Manchin told "Fox News Sunday" that he always has made clear he had reservations about the legislation and that now, after five-and-half months of discussions and negotiations, "I cannot vote to continue with this piece of legislation."The White House had no immediate comment.