I have zero problem with the President blasting an activist judge. And I say that as someone who has appeared before more than I can count, including the Supreme Court. It was a garbage decision by the District Court, and if affirmed, it'll be a garbage decision by the 9th Circuit. It was never intended that courts get to decide which foreigners get to enter our country. That is up to the elected branches, and Congress expressly delegated this particular aspect of it -- the right to exclude certain groups -- to the President.
It would be a worse assault on liberty to pretend such decisions have any real basis in law.
Heck, I don't even see a legitimate legal basis to overturn a ban on new immigration even if it was expressly limited to Muslims. Non-citizens and non-residents simply do not have constitutional rights. Period.