The problem with the executive order (EO) is that Trump overstepped, and implemented procedures to deport legal permanent residents (LPRs). He can’t do that, because Congress established the ground for removal in § 1227 and the process for removal in § 1229a. The President cannot override existing legislation, and LPRs have already entered the United States after having been throughly vetted. He can’t use his EO to sidestep the requirements of the law on LPRs, and four or five federal judges have agreed. I’m not aware of any that have upheld the EO as of yet.