On CNN’s State of the Union Sunday, the leading U.S. authority on the COVID-19 pandemic made some grim predictions about the course of the novel coronavirus as it rages through communities within the United States.

Dr. Anthony Fauci, the longtime director for the National Institute of Allergy and Infectious Diseases and emerging face of American leadership in the fight against the virus, estimated that the U.S. may see between 100,000 and 200,000 deaths from COVID-19, the deadly disease caused by the novel coronavirus. A deeply-respected authority on viral diseases, Fauci assisted in guiding the federal response to SARS, MERS, Ebola and now the novel coronavirus.

Fauci cautioned that these estimates are based on models and a model is only as accurate as the assumptions that go into building it. An extreme worst-case situation in which the coronavirus causes millions of American deaths remains “not impossible but very, very unlikely.”

“Whenever the models come in, they give a worst-case scenario and a best-case scenario,” Fauci told CNN’s Jake Tapper. “Generally, the reality is somewhere in the middle. I’ve never seen a model of the diseases that I’ve dealt with where the worst case actually came out. They always overshoot.”

Fauci believes that the U.S. is likely going to have “millions of cases” but broadly cautioned against relying on modeling estimates while still stressing the extreme risk the virus poses.

“I just don’t think that we really need to make a projection when it’s such a moving target that we could so easily be wrong and mislead people,” Fauci said. He added that outbreaks in New York, New Orleans and other areas with “serious problems” remain worrisome, indicating that the data at hand is plenty of cause for concern.

As of Sunday morning, 2,197 people in the U.S. have lost their lives fighting the virus, with 125,313 confirmed cases in the country to date according to data from Johns Hopkins University. The number of actual cases of the virus on the ground is likely substantially higher, as testing challenges continue to trouble some parts of the country and many mild or asymptomatic cases go untested.