Dr. Anthony Fauci, the nation’s leading expert on infectious diseases, is widely respected for his ability to explain science without talking down to his audience — and lately, for managing to correct the president’s pronouncements without saying he is wrong.

President Trump said that drug companies would make a coronavirus vaccine ready “soon.” Dr. Fauci has repeatedly stepped up after the president to the lectern during televised briefings or at White House round tables to amend that timetable, giving a more accurate estimate of at least a year or 18 months.

Mr. Trump said a “cure” might be possible. Dr. Fauci explained that antiviral drugs were being studied to see if they might make the illness less severe. The president also said the disease would go away in the spring. Dr. Fauci said maybe so, but because it was caused by a new virus, there was no way to tell.

Experts like Dr. Fauci should be the ones who speak to the public during epidemics, said Representative Donna E. Shalala of Florida, who was his boss during the Clinton administration, when she led the Department of Health and Human Services.