The top U.S. defense official is receiving several briefings per week about what officials deem the exceedingly unlikely possibility of Russia using its nuclear arsenal.

Defense Secretary Lloyd Austin is meeting with the military’s general in charge of monitoring U.S. nuclear weapons and defenses two or three times a week, sources told CNN. But officials express skepticism that Russia will follow through with its threats of using nuclear arms, putting the odds Russian President Vladimir Putin will do so at around 1%.