Republican presidential nominee Donald Trump looks on during the Presidential Debate at Hofstra University on September 26, 2016 in Hempstead, New York.

Republican presidential nominee Donald Trump looks on during the Presidential Debate at Hofstra University on Sept. 26, 2016, in Hempstead, New York.

Photo: Joe Raedle/Getty Images

After Hillary Clinton attacked Donald Trump’s rhetoric on nuclear issues as reckless and dangerous, Trump pledged not to be the first to introduce nuclear weapons into a conflict. “I would certainly not do first strike,” Trump said. “Once the nuclear alternative happens, it’s over.”

That may seem like common sense, but it’s actually a commitment that President Obama has been reluctant to make. The Pentagon argues that unless the U.S. is prepared to threaten a nuclear strike, it is less likely to deter Russian and Chinese aggression.

Arms control advocates have been pushing President Obama to vow “no first use,” ironically in part to try and reign in a future president.