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 (1) violates federal criminal, voting rights, or campaign finance law, or is under the direction of a foreign government; and (2) interferes with any general or primary federal, state, or local election or caucus, including a candidate's campaign or a ballot measure.