President-elect Donald J. Trump has been mocked for his tweeted claim that if it were not for illegal aliens voting, he might very well have won the popular as well as the electoral vote. Is his claim less credible than the one put forth by some of Trump’s opponents that Russian hackers got into voting machines that aren’t even connected to the Internet to switch votes around? Trump puts the number at several million. Certainly the number is higher than one, considering the loosening of voting restrictions in recent years, from motor voter laws to same-day registration to handing out...