Federal agents from the US Department of Justice have searched the home of Ilhan Omar, the progressive Democratic congresswoman from Minnesota. The search reportedly forms part of an investigation into her naturalisation, the process by which she became an American citizen. Omar was born in Somalia and arrived in the United States as a refugee before building a political career there. She has been a running target for Donald Trump over the years, and the president has made no secret of his dislike for her. No charges have been announced, and officials have not spelled out what documents or claims the inquiry centres on. Citizenship granted through naturalisation can be revisited when authorities believe a person gave false information during the immigration process. The move lands in a highly charged political climate, given her prominent profile on the left and her long feud with the president. Whatever the legal outcome, agents at the door of a sitting member of Congress is a scene bound to inflame an already heated debate.