IT IS weeks such as these, in which a president displays his authoritarian instincts, that prove the wisdom and importance of the checks and balances the framers designed. Over the past several days, President Trump has threatened a member of Congress and an iconic American company, the latter for reacting rationally and predictably to Mr. Trump’s own policies.

On Monday, Mr. Trump called Rep. Maxine Waters (D-Calif.) “an extraordinarily low IQ person” and accused her of encouraging others to “harm” his supporters. “Be careful what you wish for,” he wrote forebodingly. Ms. Waters’s statement, in which she told Americans to confront Trump Cabinet members in public, may have been impolitic. But it was no call for violence. Mr. Trump, on the other hand, offered a clear counterthreat to the brutal incitement he claimed to perceive from Ms. Waters. Ms. Waters is one member of the House. Mr. Trump is the most powerful person in the country. Any threat from him is far more chilling.

Then Mr. Trump went after Harley-Davidson. The motorcycle manufacturer announced Monday that it would move some operations overseas as it sought to protect its burgeoning European sales. The European Union has targeted the firm for tariffs in retaliation for the trade barriers Mr. Trump has imposed on certain European products. The president insists that Harley-Davidson had long planned to shift overseas and is just using his gratuitous trade war as pretext, and he threatened that the company “will be taxed like never before.”

In fact, the Harley-Davidson episode is a simple lesson of the many, easily foreseen costs of ripping up trade agreements. Goods become more expensive, businesses struggle, and people who may not have realized their jobs’ dependence on trade suddenly lose. The authoritarian reaction — to bluster and bully companies into doing what the leader demands in the face of his irrational economic management — will not change the sharp financial realities Mr. Trump is imposing on companies across the country.

It used to be a core Republican principle that the government should not dictate where companies invest, in order to keep the U.S. economy the globally competitive wealth-creation machine it has been for so long. Now GOP congressional majorities do nothing as the president throws wrenches into the gears, with no discernible end game. The framers of the Constitution gave lawmakers the power to rein in the executive on such matters; they should use it.

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