By John Wagner, Jose A. DelReal and Abby Phillip, The Washington Post A roller coaster of a campaign 18 months in the making arrives Monday at a huge moment for Hillary Clinton and Donald Trump: a 90-minute debate, with much of the nation expected to tune in amid great uncertainty about what they’ll see. Virtually tied in recent national polls, both Clinton and Trump enter the debate as the two most deeply unpopular presidential candidates in modern history.