Defending Elections against Trolls from Enemy Regimes Act or DETER Act This bill makes an alien inadmissible to the United States or deportable if there are reasonable grounds to believe that the alien seeks to enter the country to improperly interfere with a U.S. election or has previously done so. Improper interference in a U.S. election is conduct by an alien that violates federal criminal, voting rights, or campaign finance law, or is performed on behalf of a foreign government or criminal enterprise. Improper interference in a U.S. election includes acts intended to (1) undermine public confidence in election processes or institutions, or (2) influence or alter the result of an election.