The government’s top infectious disease expert said Tuesday he is cautiously optimistic that there will be a COVID-19 vaccine by the end of the year or early 2021, and warned that the next few weeks will be critical to tamping down coronavirus hot spots around the country.

Dr. Anthony Fauci and other top health officials also said they have not been asked to slow down testing for coronavirus, an issue that became controversial after President Donald Trump said last weekend that he had asked them to do just that because it was uncovering too many infections.

House Energy and Commerce Committee Chairman Frank Pallone of New Jersey said during Tuesday’s hearing that Trump’s testing comment at the rally “was an extremely reckless action, and unfortunately it continues the president’s pattern of ignoring the advice of his own public health experts.”

Trump, departing the White House for a visit to Arizona on Tuesday, played down those comments, saying under his administration the U.S. is doing more testing than any other country.

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.