Tonight on The Last Word: Vice President Kamala Harris says Donald Trump is “going to lie” during the debate Tuesday evening. Also, Sen. John McCain’s son endorses Harris for president. Plus, some in the media are “sane-washing” Trump’s incoherence. And Michael Eric Dyson discusses his new book, “ Represent: The Unfinished Fight for the Vote.” Quentin Fulks and Sen. Mark Kelly also join Lawrence O’Donnell.