If the person is a US citizen, it's much harder to for the US or the president to deport that person-- it would require revoking their citizenship status (something that rarely happens except under the most extreme conditions-- usually if the person is charged with treason).
If the person is a permanent resident, that is different. There is much more leeway for either the US government or the President to not renew a green card. There is also greater latitude for the both the President and the US government to change laws governing permanent resident status.
CUNY does have a legal clinic and other resources for immigrants:
https://www.law.cuny.edu/academics/clinical-programs/immigration/
https://www.cuny.edu/about/administration/offices/communications-marketing/citizenship-now/