During last week’s Democratic National Convention, Americans heard a variety of leaders delivering different kinds of remarks, but there was a word that kept coming up. Michelle Obama, for example, explained that Joe Biden “will tell the truth and trust science.” Barack Obama soon after said Biden and Kalama Harris recognize the importance of “fidelity to facts and science.”

Biden himself told voters, “This is a life-changing election. This will determine what America’s going to look like for a long, long time. Character is on the ballot. Compassion is on the ballot. Decency. Science.”

The Democrats’ preoccupation with science came to mind late yesterday, when Donald Trump made an announcement after ignoring concerns raised by leading scientific experts in his own administration.

President Donald Trump announced Sunday his administration was providing an emergency authorization for the use of convalescent plasma to treat COVID-19, a treatment that more than 70,000 patients have already received. One day prior to the start of the Republican National Convention, Trump made the announcement in an evening news conference.

As NBC News’ report explained, at issue is a treatment that “involves taking antibody-rich blood product from recovered coronavirus patients and providing it to those afflicted with the virus.” While this treatment is already in effect, and it’s shown some promise, the evidence “remains inconclusive about its effectiveness and appropriate dosage.”

At least at this point in the research, there is no proof that plasma is an effective treatment for those infected with the virus. Eric Topol, an influential physician and scientist and director of the Scripps Research Translational Institute, told the Washington Post that he watched Trump’s press conference “in horror,” adding, “These are basically just exploratory analyses that don’t prove anything. It’s just extraordinary to declare this as a breakthrough…. All this does is jeopardize ever getting the truth.”

He’s hardly the only one thinking along these lines. Last month, the New York Times reported that three of the government’s top health officials — the National Institutes of Health’s Dr. Francis Collins, the National Institute of Allergy and Infectious Diseases’ Dr. Anthony Fauci, and the National Institute of Allergy and Infectious Diseases Dr. H. Clifford Lane — each balked at the idea of an emergency approval, concluding that the science didn’t support such a move.

But the president has a campaign to run, a polling deficit to overcome, and an inherent belief that scientific authorities are not to be trusted. Politico added last night that Trump’s latest move was made “despite scientists’ objections,” and the president’s pitch from the White House press briefing room went beyond what the evidence supports.

Trump in a brief Sunday evening news conference appeared to oversell the FDA’s assessment, claiming the agency found plasma “safe and very effective.” The agency itself said more rigorous study is needed to prove whether the treatment effective. Janet Woodcock, the head of FDA’s drug division who is now working on Operation Warp Speed, an interagency effort to accelerate coronavirus treatments and vaccines, on Friday told POLITICO that plasma has not been “proven as an effective treatment.”

That, of course, is not what Team Trump wants the public to believe. Indeed, consider the White House’s rhetoric leading up to the announcement on emergency authorization for the use of convalescent plasma. Press Secretary Kayleigh McEnany declared that this is “a major therapeutic breakthrough.” The president called it “a very historic breakthrough,” adding that plasma treatments have “proven to reduce mortality by 35 percent. It’s a tremendous number.”

It’s also a false number. The research hasn’t “proven” anything like this.

A Washington Post analysis added, “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.”

What we’re left with was less of a medical announcement and more of a pre-convention press stunt from a president looking for attention.

There’s a phrase generally known as a business truism: under-promise and over-deliver. The idea behind the maxim is simple: it’s far better to show some humility, set modest expectations, and produce impressive results than the opposite.

But as regular readers know, Trump, a little too eager to be a “cheerleader,” can’t seem to help himself. Instead of under-promising and over-delivering, the president keeps over-promising and under-delivering — showing brash confidence, setting expectations high, and producing underwhelming results.

The Associated Press’ Calvin Woodward had a related analysis a while back on the White House casting “a fog of promises meant to reassure a country in the throes of the coronavirus pandemic,” but then failing to deliver on critical ones.

That was published in April. Trump has apparently learned nothing.

This is more than a lament about a president with a strained relationship with the truth. It’s also about a leader who’s proven — and continues to prove — that his promises and assurances about an ongoing crisis are not to be accepted at face value.

It’s possible that Trump believes exaggerations and hype will instill a sense of hope. Perhaps he sees misplaced boasts as part of a self-aggrandizing strategy that will improve his political standing. Maybe the president is confused about the relevant details and doesn’t realize that his promises are unreliable.

Whatever the cause, just once, it’d be good to see Trump under-promise and over-deliver, because he’s doing a whole lot of the opposite.