Who would have thought a few years ago that the biggest problem facing the labor market today would be a lack of workers — not a lack of jobs? As recently as 2012, the unemployment rate was above 8 percent, more than twice its current rate. Since President Trump's election, nearly 4 million new net jobs have been created. The unemployment rate has tied lows unseen since the Vietnam War, when men were being drafted to fight. Black and Latino unemployment rates are at record lows. And for the first time in recorded history, there are more jobs available than...