President Donald Trump’s Thursday tweet denying the new official death toll from Hurricane Maria was not only offensive and hurtful to Puerto Ricans who suffered through the storm ― it was also potentially dangerous. Denying the full extent of the storm’s damage prevents the country from learning much-needed lessons to prevent future fatalities, as one expert noted.

In one tweet, Trump accused Democrats of inflating the figure to make him “look bad.”

“If a person died for any reason, like old age, just add them onto the list. Bad politics,” he wrote.

Scott Knowles, a professor and disaster historian at Drexel University in Philadelphia, said Trump’s denial is a political move that undermines the full impact of not just Maria but of disasters in general and the way we account for them.

“This is inherently political, because the scale of the disaster will determine what lessons we learn from it,” Knowles told HuffPost on Friday, noting such lessons include how the government prepares for and manages future disasters ― and how much it spends on doing so.

“Getting these more inclusive and accurate death counts correct gives us a clear picture that disasters punch down,” he said.

Late Friday — as Hurricane Florence battered the southeast U.S. and claimed at least five lives — Trump doubled down on Twitter in his denials of Maria’s death toll.

Here’s more from Knowles on why every death after a disaster needs to be counted.

This interview has been edited for length and clarity.

Mario Tama via Getty Images Mourners carry the coffin of Wilfredo Torres Rivera, 58, who died in October 2017 after jumping off a bridge into a lake three weeks after Hurricane Maria hit Puerto Rico. Wilfredo's family said he suffered from depression and schizophrenia and was caring for his 92-year-old mother in a home without electricity or water.

Is there a single, universally accepted way to conduct a death count after a disaster?

It depends on which authority you’re looking toward to answer. A number will get reported in the press, traditionally affirmed by local authorities, coroners’ offices ― there’s a duty to report when someone dies, as a legal process. But it gets murky quickly.

A lot has to do with when do you draw the timeline. When do you say we’ve stopped counting now? As we’ve seen in the court of public opinion, there’s not necessarily consensus.

But in the scientific and medical communities, are there established, agreed-upon guidelines?

Yes, absolutely. But then you have the issue of when you draw the curtain on a study.

In very good faith, people want to know the scale of a disaster quickly ― how many people died? If you’re reporting a house fire or an airline crash, that can be reported quickly and clearly. It becomes trickier in a “slow” disaster ― toxic exposure, PTSD or suicides that come later. So you get into a tricky area of how long we leave the window open.

What’s an example of an instance where a long window was needed to count deaths?

How many people died in Sept. 11? The first count, done by emergency responders and deaths certified by a coroner or medical examiner’s office, that’s important. It says that day, or in a week or month, how many died.

But there’s also consensus now ― and you can go to the [Centers for Disease Control and Prevention] guidelines ― that deaths from health exposures or conditions that were made worse, which exceed what you would expect in a time and a place, those are attributable as well.

After Sept. 11, the CDC worked to set up a World Trade Center health registry. That takes a much longer view of health effects ― attributing deaths for Sept. 11 toxic exposure, particularly for firefighters. That, to me, are the guidelines we should be looking at.

It forces us to think of disasters as not something that just happens and is over but is an ongoing process.

Scientists and medical professionals will do their count ― but it’s political when elected officials try to spin those numbers and frame it in a way to show they’ve done their job well.

How does a death count, established by medical professionals, become political?

So scientists and medical professionals will do their count ― but it’s political when elected officials try to spin those numbers and frame it in a way to show they’ve done their job well.

Trump’s attitude demonstrates the problem so clearly: Usually you don’t see a politician saying, “Nope, this is the number I saw, and anything else is a lie.” We didn’t see George Bush in 2007 saying, “I don’t like that firemen who got sick [in the aftermath of 9/11] get counted because, damn it, I did a great job.” That’s abhorrent ― and political malfeasance.

How does the number of deaths in one disaster affect planning?

If Maria was bad but only 16 people died, then people would say, “It was terrible, but, at the end, it wasn’t that bad, so should we really spend all that money on [the Federal Emergency Management Agency]?”

That number becomes a stand-in for the degree to which we take [it] seriously ― that’s what’s distressing to me.

The single most important thing is to understand that vulnerable populations suffer the most in disaster. If you just do a strict count of people who died in storm surge flooding, that gives you a number ― it might be people who didn’t evacuate or drowned trying drive off. If you extend out a bit, to include people who died, let’s say, because power went off and they require power for a ventilator, you begin to see the picture of vulnerable populations emerge.

They died in the nursing home because power went out and they died of heat exposure. Or they needed surgery they couldn’t get. They needed dialysis. There were terrible stories from Puerto Rico of people who couldn’t travel because roads were closed. Getting these more inclusive and accurate death counts correct gives us a clear picture that disasters punch down: They disproportionately affect people in low-income communities, people with poor health.

That affects how we try to pre-position materials for future disasters, how we support hospitals. It changes what emergency management is if what you’re trying to do is deal with the reality of people with chronic health issues, in nursing homes [and more].

With Hurricane Florence now hitting the coast, what are you most concerned about?

For Florence, that storm is hitting some poor counties ― I’m absolutely worried about that. Because people in those communities tend to be less trusting of law enforcement, to not have as good infrastructure in their communities. I’m worried about people in nursing homes and hospitals, and if those are not trained and prepared for it. It’s very difficult.

Would I expect something on the scale of Puerto Rico? I don’t know. But mainland infrastructure, electric infrastructure, tends to be better than what was [on the island].

Would I expect the president to try to evade responsibility in Florence? Absolutely.