There may be method in his madness. I mean, that a total Muslim ban is probably not going to work, partly because it would be bad for business and trade, and also would annoy allies, such as the Saudis, and would freak out European allies. So he has picked on 7 poor countries, who are probably not involved much in US business.
He is certainly talking to his base, whether or not the opposition will be substantial, is unclear. And the long term effects seem totally unpredictable.
And it may be a godsend to ISIS recruiters and propaganda workers, who will surely milk this as much as possible. 'We told you the US hates Muslims, now they can't even travel to the US', and so on.