For nearly 30 years, Oren Etzioni was among the most optimistic of artificial intelligence researchers.

But in 2019 Dr. Etzioni, a University of Washington professor and founding chief executive of the Allen Institute for A.I., became one of the first researchers to warn that a new breed of A.I. would accelerate the spread of disinformation online. And by the middle of last year, he said, he was distressed that A.I.-generated deepfakes would swing a major election. He founded a nonprofit, TrueMedia.org in January, hoping to fight that threat.