"There are known unknowns and unknown unknowns," Rumsfeld famously said. With the incoming Trump administration we might now say, "There are certain uncertainties and uncertain uncertainties."
If Trump gets a stimulus package in the form of infrastructure spending, it will boost GDP more than if the stimulus comes in the form of tax cuts. (The tax cuts will overwhelmingly go to the rich. A guy making $500,000 a year is less likely to change his spending in response to a tax cut that puts $1,000 more in his pocket than will a guy who makes only $5,000 a year.)
Will the stimulus - the assumed rise in deficit spending - boost the economy by 1% or by something negligible? It's uncertain because we don't really know what form the stimulus will come in.
Further complicating this, Trump has appointed Mick Mulvaney to head his Office of Management and Budget (OMB). He'll be responsible for crafting the budgets proposed to Congress. Mulvaney is a fiscal hawk who has voted against raising the debt ceiling and seems committed enough to a balanced budget that he'd shut down government for this. By contrast, Trump has promised tax cuts and boosts to defense spending and infrastructure, which will drive a big increase in the deficit.
Paul Ryan and Mick Mulvaney's desire for balanced budgets will be at odds with Donald Trump's "deficit be damned" policies. Will Trump's proposed budget deficit shrink or even become a budget surplus? It's uncertain.
Deregulation adds the most uncertainty of all. Before the Great Recession, banks were leveraged about 30 to 1. For every dollar they had in deposits, they had loaned out about $30. That gives you great returns but it makes you vulnerable to a credit crunch. Since Dodd Frank,that ratio has dropped to about 10 to 1, which makes for a much safer banking system. Now, the expectation is that a Trump administration will lower regulatory requirements and allow banks to raise that ratio again. Will the ratio go up to just, say, 12 or 15 to 1? That ratio might still be reasonably safe but raise profits nicely. Or will the ratio be allowed to rise all the way to 20 to 1 or even 30 to 1 again? That ratio will greatly raise profits .... and risk. Financial stocks could look really healthy even as the financial system gets sick.
Will Trump deregulation give finance a little nudge or a dangerous shove? That's uncertain.
Add to this the uncertainty inherent in Trump's trade policies. Will he actually put 35% and 45% tariffs in place against Mexico and China? If he does, WTO will probably slap on retaliatory fines and this could set off a trade war. That path would cost us millions of jobs. If he only talks about trade wars but doesn't actually impose tariffs, it could "just" result in a slowdown in trade. It's uncertain.
And then there is the policy with undocumented workers. Will he actually deport 11 million people? If so, that will crush growth in aggregate demand here in the US and crash house prices. It's uncertain.
Economics is always uncertain but the Trump Administration has added more uncertainty to that than any that I can remember. And perhaps inherent in that uncertainty is an uncertainty about what Trump's victory will mean for the future identity of the Republican Party.