NEW YORK — Donald Trump is shaking up his campaign's leadership amid flagging poll numbers, NBC News has learned. Kellyanne Conway — already a senior adviser to the campaign — told NBC News she has been promoted to the role of campaign manager. She confirmed that Paul Manafort will stay on as campaign chair but said Stephen Bannon, the co-founder of conservative Breitbart News, will come on board as campaign CEO. The moves were first reported by The Wall Street Journal and mark yet another round of internal shakeups for a campaign that seems to be struggling to find consistent...