Federal Reserve Chairman Jerome Powell said last month that the U.S. is experiencing “a remarkably positive set of economic circumstances.” The superb numbers speak for themselves, but who gets the credit?

For eight years under President Obama, the growing burden of government suppressed the economic recovery that should have followed the recession of 2008-09. Mr. Obama nonetheless has claimed responsibility for today’s boom, asking Americans in September to “remember when this recovery started.” Yet it wasn’t until President...