happen. >> reporter: but in signs he may stop short of military action, the president announced the administration will impose new sanctions on iran. and he took a swipe at gop senator, lindsey graham, who's pressing mr. trump to get tough. >> ask lindsay. ask him, how did going into the middle east, how did that work out? and how did going into iraq work out? so we have a disagreement on that, and you know, there's plenty of time to do some dastardly things. >> reporter: unlike his combative predecessor, john bolton, o'brien was much more measured when asked what advice he'll give the president. >> any advice i give the president will be something i give him confidentially, but we're monitoring that situation closely. >> reporter: o'brien appears to have won his new job in part by heaping praise on president trump. >> the president has had unparalleled success in bringing americans home without concessions. >> reporter: but in the past, o'brien had been a trump critic, writing in 2015 that president trump had been playing out how chummy he will be with vladimir