As a Representative in the General Assembly, and while serving as a judge, Spalding was a member of the Democratic party, but throughout the 1840s he found his personal views increasingly at odds with the Party's position on slavery. While Spalding never advocated the interference of slavery in states in which it already existed, he believed that under no circumstances should slavery be extended into the territories. In 1847, Spalding delivered a speech in Akron in which he argued that "if the evil of slavery had been restricted, as it should have been, to the thirteen original states, self interest might have led to the extinction of practice long before now." Spalding's advocacy against the spread of slavery drew the attention of the Free Soil Party. In 1849, local Free Soil leaders invited Spalding, who was still a Democrat, to give a speech at a party convention in Cleveland. In his speech, Spalding maintained that he was still a strict party man, but his speech was particularly critical of southern democrats. Spalding continued to argue that slavery should not be extended into the American territories and closed his remarks with a call to Free-Soilers to "stand fast" in their beliefs. In 1850, Spalding left the Democratic Party for the Free Soil Party. His primary motivation behind this decision was the Party's support of the Fugitive Slave Act of 1850, which he felt made the Democrats a "pro-slavery" party.