In any election, it’s hard to know whose word to trust. And in a polarized country, many Americans distrust any information that comes from the other side of the political divide. That’s why the criticism of Donald Trump by those who served with him in the White House and by members of his own party is so striking. Dozens of people who know him well, including the 91 listed here, have raised alarms about his character and fitness for office — his family and friends, world leaders and business...