PRESIDENT TRUMP is promising a civil war within the union he is supposed to lead.

“If the Democrats are successful in removing the President from office (which they will never be),” the commander in chief tweeted this weekend, roughly quoting the right-wing pastor Robert Jeffress on the “Fox & Friends” Sunday show, “it will cause a Civil War like fracture in this Nation from which our Country will never heal.”

The outrageous declaration is only one among many disseminated from the digital bully pulpit over the past few days. “Arrest for Treason?” Mr. Trump suggested of Rep. Adam B. Schiff (D-Calif.), who is heading up the impeachment inquiry in the House. “Was this person SPYING on the U.S. President? Big Consequences!” he warned the person who blew the whistle on his extortionary phone call with Ukrainian President Volodymyr Zelensky. “You know what we used to do in the old days when we were smart? Right? The spies and treason, we used to handle it a little differently than we do now,” he said at a private event with diplomatic officials last Thursday.

These missives might seem to distract from the substance of the Ukraine matter, which perhaps is what Mr. Trump intends. They muffle the roar of misconduct and seize control of the narrative. But the threats can’t be ignored, because in one respect, they are the substance. The president stands accused of attempting to strong-arm another nation to sabotage a political rival, and with trying to cover it up. Now he means to menace Congress, anyone else with knowledge of his misdeeds and the public into not holding him to account.

What whistleblower in the future will come forward knowing the reward will be demonization and even potential prosecution? What does this say to aides or other officials who could speak to investigators as they probe the matter? Most Republicans are already far too reluctant to condemn Mr. Trump’s actions, much less do anything about them. Democrats, too, fear how far a man who cares nothing for the rule of law will go to mobilize his supporters against anything that imperils his presidency. Now, he is showing them.

Already, amateur Internet “sleuths” are scrambling to unmask the person who wrote the complaint released late last week. Two pro-Trump activists claim they are offering a $50,000 reward for the details. The president himself told reporters Monday that “we’re trying to find out” the whistleblower’s identity. Mr. Trump has winked at violence before. No wonder a lawyer for the whistleblower wrote to leaders of the congressional intelligence committees Saturday to say there were “serious concerns for our client’s personal safety, as well as for others connected to this matter.”

The only response to the president’s attempt to cow the country into letting him get away with abusing his office is not to let him get away with abusing his office. Congress and the nation must make Mr. Trump answer for his undemocratic intimidation tactics and for the bigger scandal he is using them to obscure.

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