Illegal alien is a legal term in the U.S.
Is a misdemeanor a crime?
https://www.law.cornell.edu/uscode/text/8/13258 U.S.C. § 1252c - U.S. Code - Unannotated Title 8. Aliens and Nationality § 1252c. Authorizing State and local law enforcement officials to arrest and detain certain illegal aliensThe term "alien" is used all over these laws.
8 U.S. Code § 1325 - Improper entry by alienAny alien who (1) enters or attempts to enter the United States at any time or place other than as designated by immigration officers,...
shall, for the first commission of any such offense, be fined under title 18 or imprisoned not more than 6 months, or both, and, for a subsequent commission of any such offense, be fined under title 18, or imprisoned not more than 2 years, or both. If you have been deported and sneak back in, it's a felony crime? subject to criteria - Penalty is harsh.10 years, 20years
https://www.law.cornell.edu/uscode/text/8/1326
8 U.S. Code § 1326 - Reentry of removed aliens
(b)Criminal penalties for reentry of certain removed aliens