Clay's proposal ignited an eight-month debate in Congress and led John C. Calhoun to threaten southern secession. He warned the North that the only way to save the Union was to "cease the agitation of the slave question," concede "to the South an equal right" to the western territories, return runaway slaves, and accept a Constitutional Amendment that would protect the South against northern violations of its rights.
Opposition to compromise was fierce. Whig President Zachary Taylor argued that California, New Mexico, Oregon, Utah, and Minnesota should all be admitted to statehood before the slavery question was addressed--a proposal that would have given the North a ten vote majority in the Senate. In July 1850, northern and southern Senators opposed to the very idea of compromise joined ranks to defeat Clay's plan. The following letter reveals just how uncertain the future of Clay's compromise proposals appeared.
Calhoun is dead, therefore his want of popularity will be no longer in our way. Our old friend Genl. [Lewis] Cass has been released from his instructions to vote for the Wilmot proviso; indeed that proposition I think is dead. What kind of settlement of the slavery question will be made I can not tell.
But California will be admitted as a state, governments for the territories without the proviso, a fugitive Slave Bill, etc.