Hines led sixty men from Toronto , Ontario , on August 25 , 1864 . They arrived during the Democratic Party National Convention held in Chicago that year . The Copperheads had told Hines to wait until that time , as they said that 50,000 Copperheads would be there for the event . However , encountering Copperhead hesitation to assist Hines and his force , and with Federal authorities apparently knowledgeable of the plot , Hines and his men were forced to flee Chicago on August 30 , 1864 . Many of the men thought Anderson may have been a double agent , forcing him to leave the group . A second attempt to free the Camp Douglas Confederate prisoners occurred during the United States Presidential Election of 1864 , but that plan was also foiled
Democratic Party National Convention
1864 Democratic National Convention
Thomas Hines