Thomas was the sole dissenter in Hamdi v. Rumsfeld, which struck down the detention of a US citizen held in Guantanamo without trial. He's an intense believer in the power of the executive over the border and national security.

(This is not totally clear cut. Controlling entry across the border is an issue uniquely within the President's powers. I think the due process issue overrides that for immigrants who have been granted visas and green cards, but I could see Thomas being "unitary executive" enough to see differently.)

The point is that the executive is constrained within the laws passed by Congress, and there is a law (https://en.wikipedia.org/wiki/Immigration_and_Nationality_Ac...) that clearly makes this not ok to do.

If the supreme court starts upholding executive orders over standing law, I'd be terrified.

Which law does it violate?

All the complaints rest on the Immigration and Nationalization Bill of 1965 (https://en.wikipedia.org/wiki/Immigration_and_Nationality_Ac...), which from a high level makes it pretty clear that you cannot discriminate by nation of origin/birth.

Thanks for that reply. It looks like the text of the relevant law is here: https://www.law.cornell.edu/uscode/text/8/1152

The law as written references a lot of other sections, but it seems pretty straightforward. My interpretation is that Trump's order is illegal.

After thinking about it for a while, I realized the law is about issuance of visas. Trump is disallowing people with valid visas from entering the country. It's not clear to me that there is a conflict here.

Good on you for actually reading the law rather than just skimming Wikipedia like I did.

I'm going to defer with the ACLU's assertion that it's unconstitutional/illegal because I trust them and they know a lot more about the law than I do. Here's their explanation for why they think it's illegal: https://www.aclu.org/blog/speak-freely/well-see-you-court-wh...

This past election season has taught me that you really can't trust anything written anymore. If you really want to understand you have to follow the links to source material. It's time-consuming.