DEARBORN, Mich. -- It is here in the industrial Midwest, not in the South, where Ted Cruz's audacious theory of the 2016 race was supposed to be put to one of its most important tests. Michigan's primary on Tuesday -- and especially what happens that day in the Detroit suburbs that in 1980 were ground zero for a new political species, "Reagan Democrats" -- will answer this question: Can Cruz locate and motivate legions of recently nonvoting conservatives, millions of them nationwide, especially whites without college experience, who can be pulled back into voting in numbers sufficient to determine the...