The biggest reality check recently has come from economist Robert Gordon in his book, The Rise and Fall of American Growth. Trump has surged into the GOP lead by promising to “make America great again,” and Sanders has called for a revolution against plutocracy to restore the middle class to its former standing and security. But Gordon argues in effect that we need to get used to just being an OK Nation. He concludes that the waves of innovation that gave us indoor plumbing, electricity, automobiles and computers may be a one-time blip in history that might not be repeated in the future. Like the historian of technology Vaclav Smil and David Edgerton, the author of The Shock of the Old: Technology and Global History Since 1900 (2006), Gordon argues that the second industrial revolution in particular, based on electricity and internal combustion engines, transformed existence much more than anything before or since, including the over-hyped the information revolution. The one-time transition from horse-drawn vehicles to automobiles was fundamental; the ongoing transition from human-driven cars to robocars is merely incremental.

Gordon may be too pessimistic. But even somewhat higher levels of productivity growth than he projects are unlikely to produce growth of the U.S. gross domestic product at historic rates, because of slowing labor force growth in an aging American population.

Yet that hasn’t stopped a bidding war of unrealistic promises, beginning with Jeb Bush’s claim that his economic proposals could raise U.S. annual GDP growth from 2.5 percent in 2015 and 2.4 percent in 2014 to 4 percent—a rate much higher than the rate under Obama (2.1 percent), George W. Bush (1.6 percent), Bill Clinton (3.7 percent), George H. W. Bush (2.0 percent), and Ronald Reagan (3.4 percent). Not to be outbid, Mike Huckabee claimed that his campaign proposals could ignite 6 percent growth. So did Donald Trump.