The petitioner, when obtaining a driver's license in Minnesota, did not attest to being a US citizen, but nevertheless, was registered to vote by the state and mailed a voter registration card.  The petitioner subsequently voted in an election.  In subsequent removal proceedings, she was deemed inadmissible for her unlawful voting, and her application for adjustment of status was denied.  The Court rejected her invocation of the defense of "entrapment by estoppel."  The Court noted that the sign in logs at the voting booths required the person to affirm that they are a US citizen.  

The full text of Chernosky v. Sessions can be found here: