U.S. District Judge Ruben Castillo will join the national law firm Akerman LLP as a partner after retiring from Chicago’s federal trial bench near the end of this month.In a statement released to the public and a separate message emailed to members of the “court family” on Monday, Castillo said he sent his formal resignation letter to President Donald Trump.He previously consulted with U.S. Sen. Richard J. Durbin, D-Ill., Castillo said in the email and Durbin’s office “will make every effort …