Trump’s Vaccine Ambitions Contradict His Own Health Experts

President Donald Trump once again promised that a Covid-19 vaccine for Americans could be ready within weeks, a timeline faster than has been deemed possible or likely by the scientific agencies overseeing the effort and the companies developing the products.

Trump’s optimistic promises have left him in a battle with the realities of time, the deadline of the election, and the increasing skepticism of the stock market that he frequently cites as a barometer of his success. On Thursday, stocks continued a two-day slide, underscoring the skepticism on Wall Street that a vaccine is near.

On Tuesday, Trump said ...