WASHINGTON — President Trump on Tuesday added his former White House aide, Omarosa Manigault Newman, to the growing list of African-Americans he has publicly denigrated on Twitter, calling her “that dog” and a “crazed, crying lowlife” in the wake of her allegations against him of mental deterioration and racism. Even for a president who consistently takes to Twitter to assail his adversaries, the morning tweet about Ms. Manigault Newman was a remarkably crude use of the presidential bully pulpit to disparage a minority woman who once served at the highest levels in his White House. The tweet reprised Mr. Trump’s...