Some 20 million Americans in primaries and caucuses will take part in selecting the Republican presidential nominee. One person will choose the vice presidential nominee. This has long struck me as absurd: One person choosing someone who, as a result, might become president for as long as 10 years. But just about everyone in politics says it's the only proper way. Over the last 25 years, presidential nominees of both parties have engaged in conscientious consultation and have mostly made pretty good choices. No more picks at five o'clock in the morning to meet a convention deadline. For even longer,...