Sean Spicer on Tuesday badly fumbled one of the major riddles of World War II: Why didn’t Hitler use the thousands of tons of lethal nerve agents that German chemists had invented and military leaders had readied for battlefield use, including sarin, the deadly gas that recently killed scores of Syrian civilians, children among them?

“It’s a real mystery,” said Raymond A. Zilinskas, director of the chemical and biological weapons nonproliferation program at the Middlebury Institute of International Studies in Monterey, Calif. “There’re a lot more questions than answers.”

During the war, the deadly agents could have dealt a major blow to the Allies, who had no knowledge of the lethal arms. According to the Army’s textbook on the medical effects of chemical weapons, German attacks with sarin and tabun, another nerve agent, “would have been devastating and might have altered the outcome of that conflict.”

Mr. Spicer, the White House press secretary, touched off a global outcry after suggesting that President Bashar al-Assad of Syria was guilty of acts worse than Hitler, and claimed that the Nazi leader had not used chemical weapons, ignoring the use of gas chambers at death camps during the Holocaust. Mr. Spicer later apologized.