"Gen. John Hyten, now the nation's No. 2 military officer, told an audience at a military forum in 2017 that leaders would not obey an illegal order and can advise the president before launching." https://www.politico.com/news/2021/01/08/pelosi-trump-take-away-nuclear-codes-456529

This DoD source is, I think, wrong? Unless he has telepathic insight into the mind of the (and every) president, it's not clear how he can draw this confident conclusion about how the arsenal "would or could be used in the absence of a direct threat"
https://www.politico.com/news/2021/01/08/pelosi-trump-take-away-nuclear-codes-456529

Now this is very interesting. "A senior military official stressed on Friday that troops have been taught to recognize and disobey illegal orders, particularly those at U.S. Strategic Command, which oversees America’s nuclear arsenal" https://www.politico.com/news/2021/01/08/pelosi-trump-take-away-nuclear-codes-456529 cc @wellerstein

"We analyze U.S. nuclear policy documents and argue that major changes must be made if U.S. nuclear war plans are to conform to these principles of just war doctrine and the law of armed conflict." https://www.mitpressjournals.org/doi/abs/10.1162/DAED_a_00412?journalCode=daed& via @Joshua_Pollack

"As General Michael Hayden...noted, the [nuclear] system “is designed for speed and decisiveness. It’s not designed to debate the decision.” Long-range missiles attacking the United States from Russian territory could reach US territory in ~30 minutes" https://fas.org/sgp/crs/natsec/IF10521.pdf

. @CRS4Congress: "The President does not need the concurrence of either his military advisors or the U.S. Congress to order the launch of nuclear weapons. In addition, neither the military nor Congress can overrule these orders." https://fas.org/sgp/crs/natsec/IF10521.pdf

Colin Powell: "I was the chairman of the Joint Chiefs of Staff and I can tell you for sure that if something like this ever happened and someone suddenly said, 'We want to use a nuclear weapon,' they would never get near it." https://www.politico.com/news/2021/01/08/pelosi-trump-take-away-nuclear-codes-456529