another possible staff shakeup at the white house. nbc news has learned that national security adviser h.r. mcmaster could be replaced as early as the end of this month, but this morning, white house press secretary sarah sanders disputed there was any plan for mcmaster's departure. joining me now, nbc news senior national security analyst, michael lighter, former director of the national counterterrorism center. thank you so much. great to see you. >> great to be here. >> let's just talk about this and the implications of it. we know that there have been some tensions simmering between mcmaster and the president, some of them have spilled out into the public. what is the significance of a potential departure and why now, do you think? >> it's really huge. the only position that this is sort of subservient to is the chief of staff.