What is Cushman afraid is being sacrificed for the sake of the compromise?

Cushman was afraid that Missouri will be a slave to be joined in the United States for the sake of the compromise.

Explanation:

Joshua Cushman was a representative of the United States diplomatic republic wrote a letter which was against the Missouri compromise. Missouri compromise wanted to balance the power between the northern part and the southern state and this could be done by allowing Maine to join the United states as a free state and Missouri as a slave state to be joined in the United States.

Cushman supported the vote of congress who was also against this compromise. With this compromise, there will be sacrifice of liberty, interest and freedom of people of Maine.