Backlash
Many members of the Democratic-Republican Party viewed opposition as treasonous or near-treasonous once war was declared. The Washington National Intelligencer wrote that, "WAR IS DECLARED, and every patriot heart must unite in its support." The Augusta Chronicle wrote that, "he who is not for us is against us."
This sentiment was especially strong in Baltimore, at the time a boomtown with a large population of recent French, Irish, and German immigrants who especially hated Britain. In early 1812, several riots took place, centering around the anti-war Federalist newspaper the Federal Republican. Its offices were destroyed by a mob. Local and city officials, all war hawks, expressed disapproval of the violence, but did little to stop it. When the editors of Federal Republican tried to return, they were removed from protective custody in a jail by a mob, on the night of July 27, and tortured; one Revolutionary War veteran, James Lingan, died of his injuries. Opponents of the war then largely ceased to openly express their opposition in Baltimore.
The Baltimore riots were the height of violent backlash during the war, whose popularity dropped through 1813 and 1814. However, after the war, when the Hartford Convention's proceedings became public just after a peace treaty was signed with Britain, there was a longer-term backlash against the Federalist Party, which became associated with secession and treason. The party never regained national predominance, fielding its last Presidential candidate in 1816 and fading away entirely by the end of the 1820s.
Read more about this topic: Opposition To The War Of 1812 In The United States