This time, the false hope started with the president’s press secretary.

In a tweet Saturday night, Kayleigh McEnany told the world that Trump would announce “a major therapeutic breakthrough” on the novel coronavirus at a Sunday evening news conference. As the president took the podium, he echoed McEnany, promising a “very historic breakthrough … that will save countless lives.”

The truth — not surprisingly — was different: Trump did not announce any breakthrough vaccine or miracle cure, but merely an emergency-use authorization for convalescent plasma, which, while promising, is neither a sure thing nor a breakthrough. Contrary to Trump’s assurances, the treatment, which uses antibody-rich plasma donated by covid-19 survivors, has not been proven to reduce mortality. Just a few weeks ago, according to the New York Times, “top federal health officials including Dr. Francis S. Collins and Dr. Anthony S. Fauci intervened” to delay the emergency authorization because of concerns that the data on plasma’s effectiveness was too weak. Even if it does work, the treatment is already widely available, so any gains from Trump’s emergency authorization will be “incremental,” according to former Food and Drug Administration commissioner Scott Gottlieb.

These facts didn’t stop Trump from taking credit, nor from congratulating the FDA, which “really stepped up,” according to the president. It was a far cry from Saturday morning, when Trump accused “the deep state, or whoever, over at the FDA” of deliberately delaying vaccines and therapeutics until after Election Day — making clear, as if there were any doubt, that the president had been wielding this latest conspiracy theory only for his own political reasons.

That’s par for the course for this president, of course, who loves few things more than playing games with conspiracy theories. On Thursday, Trump told Fox News’s Sean Hannity that “we’re going to have sheriffs, and we’re going to have law enforcement” at polling places to combat voter fraud. When critics pointed out that federal law enforcement at the polls would intimidate voters and would be likely to violate the law, White House chief of staff Mark Meadows pretended that “what the president was really addressing was to make sure that if you want to show up and vote in person, we’re going to make sure that that is safe.” Sure. But it’s all empty posturing anyway: Even acting DHS secretary Chad Wolf — who had no qualms about sending federal law enforcement in unmarked vehicles to Portland — agreed Sunday that the department doesn’t have the authority to deploy officers to polling places.

Another wink to conspiracy theories came Wednesday, when Trump was asked about the QAnon movement, which believes Trump is fighting a worldwide cabal of Satan-worshippers, sex traffickers, pedophiles and/or cannibals. Rather than debunk the movement, as any normal president would do, Trump claimed, “I don’t know much about the movement other than I understand they like me very much.” It’s nigh impossible that the cable-news-obsessed Trump is actually ignorant of QAnon. Worse, his refusal to disavow it has only bolstered adherents, who have been linked to arson, assault and even murder. But they vote for Trump, and in the president’s mind that, well, trumps all.

Still, as scary as these indulgences of conspiracy theories are, nothing is more dangerous in this moment than false hope. Convalescent plasma is just the latest case of Trump promising breakthroughs or downplaying the threat. First came weeks of promises that “it’s going to work out fine” and “the coronavirus is very much under control.” Then came months of touting so-called cures such as hydroxycholoroquine. And then came claim after claim that conditions were safe for states and businesses to reopen.

The costs of stoking these false hopes are most obvious in the millions who have become sick or died after foolish reopenings. On top of that, though, must be added the confusion wrought by the president’s repeated misstatements, the loss of confidence in experts whose advice the president rejects and the demoralization of millions who thought, based on the president’s word, that happier times were just around the corner, only to have the rug pulled out from under them.

In offering more false hope on the eve of the convention renominating him for president, Trump gave us the best reminder why doing so is such a grave mistake.

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