One person has lost an election to Donald Trump. Hillary Clinton wrote a book about that painful experience, “What Happened.” Note to all those Democratic presidential contenders working to avoid repeating Mrs. Clinton’s failure: Review her chapter called “Country Roads.”

Even liberal commentators are expressing some alarm over the mass hara-kiri the Democratic field committed on stage in last week’s debate, at least on the issues of health care and immigration. They are gently warning that 150 million Americans have private...