In November 1865, Frank Blair attempted to vote at a municipal election to elect the St. Louis County auditor and a judge for the 6th Judicial District of St. Louis County. As he prepared to deposit his ballot, he offered an affidavit containing his own oath of allegiance to the United States and the State of Missouri. However, the election judges rejected Blair's ballot, stating that while the 1865 state constitution required an oath as a prerequisite for voting, Blair offered a different oath, not prescribed by the constitution. Failure to take the prescribed oath meant Blair was not entitled to vote, according to election judge Stephen Ridgeway's petition.

Blair sued for his franchise privileges, but lost at both the St. Louis Circuit Court and the Missouri Supreme Court. A final appeal to the United States Supreme Court failed to support Blair's challenge to the constitutional oath of loyalty. Ultimately, the “Ironclad Oath” was removed from the Missouri constitution in 1870.

http://www.sos.mo.gov/archives/resources/civilwar/BlairVRidgely.pdf