"The problem for the Trumpians is that we've had eight years of recovery," Lee Branstetter, a professor of economics at Carnegie Mellon University, told Business Insider. "Now unemployment is well below 5%, and there's just not a lot of slack in the US labor market. ... It's essentially mathematically impossible to get the growth they're talking about."

You may be wondering where Trump and company got the idea that deregulation, tax cuts, energy policy, and the like can juice GDP growth.

Blame former President Ronald Reagan.

A lot of Trump's ideas — like increasing the defense budget, cutting taxes, and slashing budgets for tiny programs — come from the Reagan playbook.

GDP growth was stronger during his presidency, but it wasn't because of those policies. Again, it was a function of demographics. Reagan, more like Obama, took office during a deep recession, when there was plenty of slack in the labor market.

"Back in the '80s, baby boomers were coming into the labor force, and many women were entering the workforce for the first time, too," Branstetter said. "That resulted in the workforce increasing by 1.7%, and because of technological advancement, productivity growth was running at about 1.7% as well."

That's where you get your 3% GDP growth number.

Tax cuts and deregulation would help only if they spurred people to hire more workers, but they also could hurt. Deregulation was a big factor in our last financial crisis, for example.

And as for tax cuts, according to the Center on Budget and Policy Priorities, states that enacted big tax cuts haven't seen strong job growth. The evidence that they help with jobs just hasn't materialized.