Can I Do a Muslim Ban Legally?

Rudy Giuliani said Donald Trump came to him and said, how do I do a Muslim ban legally? And this is what we got. That's another thing that's going to look really bad in court when they're saying this is not discriminatory. But so what they've done is they've come up with like a list of countries that have a lot of Muslims in them. They can cite to lists that pre-exist the Trump administration.