President Donald Trump has signed off on a plan to fire Dr. Marty Makary, commissioner of the Food and Drug Administration, after a series of clashes over vaping, oversight of the abortion pill and a series of new drug application denials that rattled biotech companies, according to a person briefed on the matter, who was not authorized to discuss it publicly. Makary had a high profile for an FDA commissioner, appearing frequently on television and podcasts to sell the work he was doing at the agency on improving the food supply, speeding up some drug approvals and trying to restore agency morale after thousands of staff members left. He tried to walk the tightrope between the business-friendly Make America Great Again movement, pledging to get rid of regulations that slow down innovation and to attract more drug trials to the United States. He was an ally of Health Secretary Robert F.…