A Douglas County Deputy District Attorney who is running for a statehouse seat has a long history of prosecutorial missteps and choices that appear to belie his campaign’s tough-on-crime theme. 23rd Judicial District Senior Deputy District Attorney Nate Marsh is looking oust state Rep. Bob Marshall (D-Highlands Ranch), one of the few Democrats elected in blood red Douglas County. Marsh has endorsements from his former boss (and another former Co…