The other day all the major new outlets were covering a story about Elizabeth Warren saying on the campaign trail in Iowa that Donald Trump “might not even be a free person” but rather in jail at the time of the 2020 Presidential election.

Call this phenomenon the “hypothetical news.” Donald Trump might launch a preemptive nuclear attack on North Korea. Donald Trump might withdraw from NATO. Donald Trump might fire his Chief of Staff. Donald Trump might be crazy.

More subtle examples of hypothetical news are: there is “widespread concern on Wall Street” that Donald Trump might fire Fed Chairman Powell; or “White House sources say” that Donald Trump is considering firing Fed Chairman Powell.

The ones quoting Elizabeth Warren or unnamed White House sources are the most insidious because they masquerade as real news. But now here comes one that would be really effective: Yesterday in an exclusive interview, President Donald Trump denied he was considering firing Robert Mueller. We now switch to a group of former prosecutors discussing what effect it would have on the investigation if he did fire Mueller. Next, an interview with prominent Democrats and Republicans on Capitol Hill discussing what effect it would have on the prospects for impeachment if President Trump were to fire Mueller, followed by an exclusive interview with a senator who has introduced legislation to protect Mueller from being fired by President Trump.

None of this has actually happened, but on many days, there isn’t enough of what has actually happened to fill the 24-hour news cycle, so cable news and other media speculate about what might happen.

Donald Trump is a favorite target of hypothetical news, but these techniques are also popular in other areas. Fruit juices “may” contain high levels of dangerous metals such as arsenic, lead, and cadmium, Consumer Reports states breathlessly in its latest issue.

This after their testing was unable to find any dangerous levels that violate FDA’s already precautionary limits. But other samples “might” contain higher levels because like anything else grown in soil, fruit juice does contain trace levels that can be detected by modern technology that can find substances down to the parts per billion.

Hypothetical news is even more insidious than its close cousin, “fake news.” At least fake news can be proven to be false, as a recent story by BuzzFeed was when Robert Mueller’s team disavowed it. But as government propaganda ministries have known for generations, disinformation is effective even when it is false. The initial story enters our minds and affects our mental images even if it is later disproven. “A lie can travel halfway around the world while the truth is still putting on its shoes” wrote Jonathan Swift, the author of Gulliver’s Travels. And that was prior to the internet.

But it isn’t merely that both fake news and hypothetical news are covered more prominently than later information showing that the alleged problem doesn’t really exist. Modern brain science teaches that every experience creates permanent biological changes in the structure of the brain. Unlike the memory of a computer, once an impression is formed in the human brain, it is not possible to erase it. The report that it is false simply creates a second impression in the brain linked to the first. The more times we hear something repeated, the more changes in the brain and the stronger the impression. A visual impression contains about 100 times more data and therefore more storage in the brain then merely hearing or reading something. Maybe a picture isn’t really worth a thousand words, but it is worth at least a hundred.

Our beliefs are formed out of the sum total of the impressions in our brain filtered by our pre-existing ideologies or maps of the way that we think the world works. Seeing President Trump deny he is going to fire Mueller after hearing many times that he is considering doing so only confirms the impression that he must be considering it. Trial lawyers have long known that if one can get a jury to imagine how something might have happened, the jurors are likely to believe that is how it did happen. Modern research into the psychology of belief calls this the availability heuristic.

The law has long known that hypothetical questions can affect beliefs and so the common law of evidence prohibits asking a hypothetical question unless there is evidence to support it. By this standard, it is legitimate to speculate that President Trump might launch a preemptive attack on North Korea to take out its nukes, because he has said that he might. Perhaps a fair and balanced story would also note that is how he negotiates. But it is not fair game to speculate that he is about to fire someone, for example, if there is no evidence to support this hypothetical.

As for juice, the availability heuristic suggests that, having first been told that it might be toxic, no matter how much evidence to the contrary is presented, many people will be scared into drinking something else. The last time the press ran a story that juice might contain trace levels of arsenic, sales went down by 40 percent. Hypothetical news does change perceptions.

Donald Elliott is Professor (adjunct) of Law, Yale Law School. Gail Charnley Elliott, a toxicologist, is principal of HealthRisk Strategies consulting firm.