Dr. Bright had headed the Biomedical Advanced Research and Development Authority, which is developing a vaccine.
The president described Dr. Bright as “disgruntled” and said on Twitter that he “never met him or even heard of him”.
But Dr. Bright told Congress that not only was the US not prepared for the pandemic, but that more was to come.
“There will likely be a resurgence of COVID-19 this fall and be greatly compounded about the challenges of seasonal influenza,” said Dr. Bright. “Without better planning, 2020 could be the darkest winter in modern history.
“First and foremost, we need to be truthful with the American people. Americans deserve the truth,” continued the scientist.
“The truth must be based on science. We have the world’s greatest scientists. Let us lead.”
His testimony highlights the ongoing struggle between science, health and diseases experts and Mr Trump political aims.
More than 80,000 Americans have now died from Covid-19, with the death count anticipated to be much higher.
Mr Bright also told the House of Representatives subcommittee on Thursday health that “lives were lost” because of government “inaction” in the early stages of the outbreak.
The same criticism has been issued against Mr Trump multiple times since the outbreak began.
Dr. Bright added that he “got no response” when he raised an internal warning about medical equipment shortage in January.