President Trump. (Jabin Botsford/The Washington Post)

IT IS easy to become inured to President Trump’s persistent, exhausting campaign to delegitimize the people and institutions unwilling to accommodate his personal desires. A skilled propagandist, Mr. Trump constantly repeats and escalates his accusations, threats and outlandish claims: The FBI is corrupt; special counsel Robert S. Mueller III is running a rigged investigation; reporters are enemies of the people. As he intends, these begin to seem normal and even plausible to Americans who want to believe him.

But his latest escalation, on Twitter on Wednesday, should not be shrugged off. “This is a terrible situation,” the president fumed about the Mueller probe. “Attorney General Jeff Sessions should stop this Rigged Witch Hunt right now, before it continues to stain our country any further.” Mr. Trump added, “Bob Mueller is totally conflicted, and his 17 Angry Democrats that are doing his dirty work are a disgrace to USA!”

Mr. Sessions, who was deeply involved in the 2016 campaign, properly recused himself from decision-making in the Russia investigation. Mr. Trump has found no such reservoir of decency; instead, he has employed a cynical and despicable strategy to chip away at Americans’ faith in bedrock American institutions with the assistance of his lawyer, former New York mayor Rudolph W. Giuliani, who in his later years seems to be trying his best to mar his legacy as a former Justice Department prosecutor.

If the country needed any more reminders that the Russia investigation exists for good reason, Facebook provided one this week. The social media giant revealed Tuesday that it shut down 32 pages and phony accounts apparently established to manipulate Americans during this year’s midterm elections. The fake accounts had attracted 290,000 followers and divisively fanned the flames of left-wing activism. Facebook could not conclusively confirm that Russia was behind the campaign, but evidence points strongly to the Kremlin. This revelation came on the heels of news that Russians last year attempted to hack into computers used by Sen. Claire McCaskill (D-Mo.).

Russia attacked the country in 2016 and helped Mr. Trump win election. Senior intelligence officials have warned for months that the Russians have not paid a high enough price for their 2016 election hacking, that they have not been deterred and that they are not done meddling. Now concrete examples of more Russian interference appear to be emerging.

Instead of focusing on defending the country from further attack, the president has resisted and undercut efforts to evaluate what happened. It may be understandable for him to dislike anything that seems to question the legitimacy of his remarkable 2016 victory, which took most political professionals by surprise. But it is not acceptable to act on that sentiment by trashing American law enforcement professionals and journalists. He might see this as a win for his political brand. But he is hurting the country. So, too, are Republicans such as national security adviser John Bolton when they chime in on the “witch hunt” rhetoric.

By all appearances, Mr. Mueller is conducting the sober, effective investigation that the government asked him to conduct. He does not leak. He does not grandstand. He does his job. Let him get on with it.