The last time the US dramatically expanded its force of immigration officers, major problems arose. Some border agents recruited in the 2000s turned out to be cartel members. One kidnapped and raped three women in his custody. Two others were convicted of off-duty murders. Now, as Donald Trump vows to build “the largest deportation operation” in history and kicks off a massive recruitment spree, human rights advocates and former Department of Homeland Security (DHS) officials are warning that misconduct and violence by officers could increase as a result. Bolstered by an unprecedented $170bn in funding for Immigration and Border Enforcement,...