He writes at WaPo:
While comparisons between Donald Trump and Mussolini or Hitler are overwrought, Trump’s rise does illustrate how democratic processes can lose their way and turn dangerously toxic when there is intense economic frustration and widespread apprehension about the future. This is especially the case when some previously respected leaders scurry to make peace in a new order -- yes Chris Christie, I mean you.
The possible election of Donald Trump as president is the greatest present threat to the prosperity and security of the United States. I have had a strong point of view on each of the last ten presidential elections, but never before had I feared that what I regarded as the wrong outcome would in the long sweep of history risk grave damage to the American project.
The problem is not with Trump’s policies, though they are wacky in the few areas where they are not indecipherable. It is that he is running as modern day man on a horseback—demagogically offering the power of his personality as a magic solution to all problems—and making clear that he is prepared to run roughshod over anything or anyone who stands in his way....
Nothing in the way he campaigned gave Richard Nixon a mandate for keeping an enemies list or engaging in dirty tricks. If he is elected, Donald Trump may think he has such a mandate. What is the basis for doubting that it will be used?...What will a demagogue with a platform like Trump’s who ascends to the presidency do with control over the NSA, FBI and IRS? What commitment will he manifest to the rule of law? Already Trump has proposed that protesters at his rallies “should have been roughed up.”...
A growing sense that a protectionist demagogue could soon become president of the United States would surely introduce great uncertainty at home and abroad. The resulting increase in risk premiums might well be enough to tip a fragile U.S. economy into recession. And a concern that the U.S. was becoming protectionists and isolationist could easily undermine confidence in many emerging markets and set off a financial crisis.