Overnight Defense: Iran sanctions back in place | Trump grants waivers to Iranian civil nuclear projects | Trump 'surprised' at question about replacing Mattis | Study pegs border deployment cost at $42M-$110M

Happy Monday and welcome to Overnight Defense. I'm Rebecca Kheel, and here's your nightly guide to the latest developments at the Pentagon, on Capitol Hill and beyond. CLICK HERE to subscribe to the newsletter. THE TOPLINE: All...