PRESIDENT TRUMP informed the country over Twitter of his positive coronavirus diagnosis at 12:54 a.m. on Friday. By morning, the Internet was already rife with conspiracy theories and other misinformation. The frenzied speculation must stop: It feeds into the insidious “infodemic” environment that the president himself helped to create.

Experts warn that last week’s revelation is fertile soil for all sorts of opportunists to plant lies, especially ahead of an election. Adversaries abroad could attempt to destabilize democracy by suggesting, for example, an elite plot to replace the president on the ballot; domestic actors might cook up tales to serve their own partisan ends. Already, wild whispers have emerged from both sides of the political spectrum: that the White House is faking Mr. Trump’s illness to distract from other scandals, such as the release of the president’s troubling tax returns; or to avoid more damaging debates; or to “prove” after a speedy recovery that covid-19 isn’t so bad after all. Now talk has turned to the severity of his case and the timeline surrounding its disclosure.

Rumormongering is equally irresponsible no matter its source, but it is especially disheartening to see such behavior from those who have spent the past months rightly bemoaning the stream of falsehoods about covid-19 coming from the Oval Office. A recent report from Cornell University found that Mr. Trump has been “likely the largest driver of the COVID-19 misinformation ‘infodemic’ ” in traditional and online media: Almost 38 percent of articles containing debunkable claims, including that hydroxychloroquine could be a miracle cure for the disease, mention the president in the context of the inaccuracies. The researchers note how damaging this misinformation can prove, whether it prompts people to attempt to treat themselves with harmful substances or reduces trust in health authorities trying to promote responsible behavior.

Of course, the president’s behavior has also had the effect of reducing trust in him. Those who today do not believe a word coming from the White House about Mr. Trump’s illness are responding to the reality that the words coming from the White House throughout this crisis have frequently been unbelievable. The problem was compounded Saturday when the president’s doctor and chief of staff offered accounts of his condition that were contradictory and incomplete. Transparency from reputable sources will prove crucial in the days to come. Yet guessing about Mr. Trump, or others infected in the administration, without any grounding in verified fact only contributes to the chaos.

Today, health misinformation and political misinformation are melding together to the detriment of our health and our politics alike. Mr. Trump may have created this mess. But those who deplore his handiwork should take care not to make our national conversation more of a shambles.

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