I love how you erroneously try to frame this.
Has nothing to do with Republicans. It is U.S. law. Section 8 U.S. Code § 1324. Bringing in and harboring certain aliens.
(iii) (Any person who) knowing or in reckless disregard of the fact that an alien has come to, entered, or remains in the United States in violation of law, conceals, harbors, or shields from detection, or attempts to conceal, harbor, or shield from detection, such alien in any place, including any building or any means of transportation;
..... an offense in which the alien is not upon arrival immediately brought and presented to an appropriate immigration officer at a designated port of entry, be fined under title 18 and shall be imprisoned
https://www.law.cornell.edu/uscode/text/8/1324
