For the past few months, a single senator — Tommy Tuberville — has blocked hundreds of promotions in the U.S. military.Karoun Demirjian, a congressional correspondent for The Times, explains what’s behind the senator’s blockade, and why military leaders say it’s becoming a threat to national security.Guest: Karoun Demirjian, a congressional correspondent for The New York Times.Background reading: Tuberville’s bid to reverse a Pentagon policy ensuring abortion access for service members has delayed the smooth transfer of power at the highest echelons of the armed forces.Here’s David Firestone of Times Opinion on Tuberville’s blockade.For more information on today’s episode, visit nytimes.com/thedaily. Transcripts of each episode will be made available by the next workday.