In 2008, Barack Obama won 26% of the evangelical vote; in 2012, he won 21%. Hillary Clinton won 16%. If she had simply replicated Obama's performance among evangelicals, she would likely be President. In his new book, Do We Have a Center? 2016, 2020 and the Challenge of the Trump Presidency, Walter Frank, author of Law and the Gay Rights Story and Making Sense of the Constitution, warns that Democrats ignore the many lessons of the 2016 campaign at their peril. "The Democrats," Frank counsels, "are in grave trouble if they don't understand exactly what happened in 2016 and all...