A new report Wednesday shows President Donald Trump's estimate that the U.S. could see "substantially under" 100,000 coronavirus deaths may be a massive underestimate because of the nation's huge incarcerated population.

Adding in the conditions of the U.S. jail system means the death toll—even with highly effective social distancing measures—could be 200,000.

That's the startling finding from a new epidemiological model released by the ACLU and researchers at Washington State University, the University of Pennsylvania, and the University of Tennessee.

"The United States' unique obsession with incarceration has become our Achilles heel when it comes to combatting the spread of COVID-19," said the ACLU.

According to the report, the Trump administration failed to take into account factors that stand to "explosively increase the loss of life" from the coronavirus in its projection.

Those factors include other nations having far lower incarceration rates and the conditions at U.S. jails, including poor healthcare afforded to those incarcerated, substandard sanitation measures, lack of social distancing, and the sheer rate of human traffic flows at the facilities. Roughly 737,900 people are in jail on any given day, including people simply unable to post bail.

Those combined factors contribute to jails being poised to serve as not just "vectors" but "veritable volcanoes for the spread of the virus," said the researchers.

The report attributes that scenario to two main pathways of transmission:

Churn of the jail population—individuals are arrested, sent to jail, potentially exposed to COVID-19, released on their own recognizance, post bail, or are adjudicated not guilty and are subsequently released. Upon release, the virus will spread through their families and communities unless the individual is quarantined.

Jail staff—staff come to work each day and are exposed to COVID-19, then return home and infect their families and communities. This vector applies to jails, prisons, and detention centers. There are ~420,000 people who work in jails and prisons in the U.S.

Failing to take those avenues of coronavirus infections into projections gives an overly optimistic estimate of total deaths in the U.S. From the report:

What our model tells us with near certainty is that ignoring jails in the public health measures taken to mitigate COVID-19 spread will result in the substantial undercounting of potential loss of life. For example, if a model that doesn't account for jails predicts that social distancing and other public health measures will keep the total number of U.S. deaths to 101,000, our model shows that that projection undercounts deaths by 98 percent. Actual deaths, once we account for jails, could be almost double, rising to 200,000.

It's still possible to avoid such a high loss of life if swift action is taken to reduce the prison population. The report outlines a number of specific recommendations for that to happen, including for prosecutors to decline to prosecute people facing low-level charges and to recommend pre-trial release unless physical harm to another person is at risk.

The researchers also called for sheriffs to release people uniquely vulnerable to COVID-19 because of an illness or other factors. Sheriffs should also "consider releasing other people in custody where the release poses no risk of serious physical harm to another person, including people held by the sheriff on immigration detainers."

Judges should also order pre-trial release without conditions, unless a person would be at imminent risk of harm, "and suspend issuance or enforcement of any bench warrants for failure to appear or technical parole or probation violations," the report added.

Slashing the number of arrests by half could have a massive impact, with the model suggesting that action could spare 12,000 human lives in jail, and 47,000 in surrounding communities.

"If we stop arrests for anything but the five percent of crimes defined as most serious by the FBI—including murder, rape, and aggravated assault—and are able to double the rate of release for those already detained, we can save 23,000 lives in jails, and 76,000 lives in communities," the researchers added.

There's no time to waste, the report says, projecting up to 18,000 lives lost if efforts to reduce the jail population are put off by even one week. So far, 133 people have died of COVID-19 while incarcerated, and the researchers expect the number togrow unless prison system reforms are enacted swiftly.

"While all of us will be impacted by inaction, communities of color will feel it most," the ACLU said in an accompanying analysis.

Black and Brown people are overrepresented in jails and prisons due to long-entrenched racial bias in the criminal legal system, as well as low-income communities. Most correctional staff are also people of color, who will return to families and communities of color while potentially carrying the virus. There is already ample evidence that Black people are dying at much higher rates in major cities across the country. We can expect even more racial disparities in COVID-19 deaths if we allow the virus to spread freely throughout jails.

"COVID-19 has already changed the way we live and function as a society in ways that would have been unimaginable just a month ago," wrote Udi Ofer, director of the ACLU's Justice Division, and Lucia Tian, the group's chief analytics officer.

"There is no reason to exclude prisons and jails from these radical changes—especially in a country that incarcerates more of its people than any other country on Earth," wrote Ofer and Tian. "It's time for the government to act in the name of public health. Failing to protect incarcerated people will hurt all of us."