Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, said on CNN's "State of the Union" Sunday that models suggest the coronavirus will infect millions of Americans and could kill 100,000–200,000, though he stressed that the projections are "such a moving target."

Why it matters: Fauci has been the coronavirus task force's most outspoken advocate for emergency social distancing measures to stop the spread of the coronavirus, sometimes contradicting President Trump's more optimistic outlook.

The U.S. reached more than 100,000 confirmed cases and over 2,000 coronavirus deaths on Saturday. The global death toll has topped 30,000, with over 680,000 cases worldwide.

What he's saying:

"There are things called models, and when someone creates a model, they put in various assumptions. And the model is only as good and as accurate as your assumptions.

And whenever the modelers come in, they give a worst-case scenario and a best-case scenario. 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 scenario actually came out. They always overshoot."

The big picture: Fauci again emphasized on CNN that Trump's plan to lift social distancing guidelines by Easter, or April 12, is not set in stone and that it will depend heavily on the availability of new tests that can give coronavirus results in 15 minutes.

These real-time tests will allow health officials to identify patients, isolate them and do "contact tracing" to locate people they interacted with, Fauci said.

He added that he doubts social distancing restrictions will be eased at the end of the White House's "15 Days to Slow the Spread" initiative this week, as Trump has suggested.

Of note: Trump has clashed with some Democratic governors like Michigan Gov. Gretchen Whitmer and said that he wants them to be more "appreciative" of the federal government.