NEW YORK CITY — Is it possible that President Trump has already beaten Sen. Bernard Sanders? Four years ago, Bernie Bros stormed Iowa and took over the Democratic caucuses. In Iowa, he came within a whisker of beating the Clinton machine. He won 696 local delegates, just 4 fewer than Mrs. Clinton’s 700. In New Hampshire, Mr. Sanders utterly swamped Mrs. Clinton. With 151,000 voters turning out for Mr. Sanders, he clobbered Mrs. Clinton by 22 percentage points. Now, fast-forward from 2016 to today. Certainly, Mr. Sanders is the clear front-runner for the Democratic nomination in a far more crowded...