WASHINGTON — The government’s top infectious disease expert Dr. Anthony Fauci is testifying Tuesday before a House committee, saying that more coronavirus testing is needed, not less. That is the opposite of what President Donald Trump said on Saturday night at his election rally.

Fauci returned to Capitol Hill on Tuesday at a fraught moment in the nation’s pandemic response. In addition to him, the heads of the Centers for Disease Control and Prevention, the Food and Drug Administration, and a top official at the Department of Health and Human Services answered questions.

Coronavirus cases are rising in about half the states and political polarization is competing for attention with public health recommendation.

"The next couple of weeks are going to be critical in our ability to address" the surge of cases in Florida, Texas, Arizona and other states, Fauci said in response to a question Tuesday.

Fauci was asked about Trump's comments at a Saturday rally in Tulsa, when he indicated that less testing was needed. Without mentioning Trump by name, Fauci said there should be "more testing, not less." 

“You have to have the manpower, the system, the testing, to identify, isolate and contact trace in an effective way," Fauci said.

All four federal public health officials said Trump hasn't asked them to slow coronavirus testing.

In prepared testimony submitted for all four witnesses, HHS told lawmakers that “the rigorous clinical testing required to establish vaccine safety and efficacy means that it might take some time for a licensed (coronavirus) vaccine to be available to the general public.”

Fauci remains "cautiously optimistic" that a vaccine will be found by the end of 2020 or start of 2021. He noted that patients develop antibodies to the virus — a sign that the human immune system is able to battle back. 

On Tuesday, Trump is scheduled to visit Arizona, a coronavirus hotspot where the rate of positive COVID tests is about 20 percent, well above the threshold for widespread transmission. His plans include addressing a “Students for Trump” rally.

Fauci has recently warned that the U.S. is still in the first wave of the pandemic and has continued to urge the American public to practice social distancing. And, in a recent ABC News interview, he said political demonstrations such as protests against racial injustice are “risky” to all involved. Asked if that applied to Trump rallies, he said it did. Fauci continues to recognize widespread testing as critical for catching clusters of COVID-19 cases before they turn into full outbreaks in a given community.

About 2.3 million Americans have been sickened in the pandemic, and some 120,000 have died, according to data from Johns Hopkins University.

Fauci, who heads the National Institute of Allergy and Infectious Diseases, was joined by CDC director Dr. Robert Redfield, FDA chief Dr. Stephen Hahn and the head of the U.S. Public Health Service, Adm. Brett Giroir.

The Associated Press contributed to this story.