But the chairman of the panel, Republican Senator Lamar Alexander, also pointed the finger at Trump, saying the president had the power to end politicization of mask-wearing that suggests "if you're for Trump, you don't wear a mask. They would follow his lead".
"Now we are seeing the consequences of community spread which is even more hard to contain than spread in a well-known physical location ..."
Fauci said it is clear that some parts of the country skipped over checkpoints or guidelines for when it is safe to reopen.
Yes, but: Fauci noted that states and localities that "did it right" regarding reopening still had individuals who engaged in an "all or none phenomenon" - disregarding social-distancing measures and face mask usage while out socially.More news: McGrath Ekes Out Victory in KY’s Democratic Primary
In places where cases are soaring, USA health officials are also considering "completely blanketing these communities with tests", Fauci said, to try to get a better sense of an outbreak.
Many US states have paused reopenings as their infection caseloads balloon.
Fauci indicated that he would support an effort to increase the production of high-quality masks in the United States and distribute them free of charge to the American public in response to a question from Vermont independent Sen.
FDA Commissioner Stephen Hahn said vaccine makers also must test their shots in diverse populations, including minorities, the elderly, pregnant women and those with chronic health problems.
Regarding a potential vaccine, Fauci said that while health officials are hopeful, there's "no guarantee" the USA will develop a "safe and effective" vaccine for the coronavirus. "We have an obligation to use all of our scientific knowledge, our regulatory framework to ensure that any vaccine that comes before us, whether for authorization or approval, meets our stringent standards for safety and effectiveness". That's less effective than many of today's vaccines but independent experts say that would be a good start against the virus.More news: Lewis Hamilton says Bernie Ecclestone comments on race 'ignorant'
He later implored Fauci for a change in tone: "We need more optimism".
"There are some states in which the leadership and the decision [to open up] was a little too precipitous", he said.
"I think there was a lot of wishful thinking around the country that, "hey it's summer".
Asked about polls showing that as many as a third of Americans would refuse a vaccine even if it's free, meaning possibly only 70 to 75 percent of Americans would be willing to get the vaccine once available, Dr. Fauci confirmed the slim chances of herd immunity in that scenario.
New Zealand declared the country infection-free on 8 June, and since then has had to contain several cases that came from worldwide travellers.More news: Cirque du Soleil files for creditor protection in Canada
The president himself has bucked conventional wisdom on slowing the spread of COVID-19, holding large in-person events as part of his reelection campaign. More than 129,000 people have died in the USA from the virus and approximately 2.68 million cases have been reported.