Christmas Day, 1861:
President Lincoln held an urgent Cabinet meeting on Christmas morning to discuss the Trent affair. The initial enthusiasm over the capture of Mason and Slidell had cooled, and serious concerns about war with Great Britain were being felt. Postmaster Montgomery Blair had been in favor of releasing the captives even before the meeting. But Lincoln himself was in favor of submitting the dispute to some form of arbitration, and holding the two Confederate envoys in the meantime. And the general feeling was still that apologizing to Britain would look like cowardice.
Secretary of State Seward, however, had written a detailed paper going over the events and examining the relevant laws, the only one to do so. His main point in the debate was that releasing the envoys was consistent with the traditional American position on the right of neutrals, and the public would accept it as such. An argument could be made that Captain Wilkes' stopping and searching of the Trent violated international law only because the Trent had not been seized and taken to a Union prize court. (However, this would have inflamed British public opinion to the point where war would have been virtually certain.) Therefore, although Mason and Slidell would be let go, no formal apology was necessary.
Into the meeting came Senator Charles Sumner, Chairman of the Senate Foreign Relations Committee. The Senator had become a hero to the North after a South Carolina Congressman had beaten him into a coma with his cane--on the very floor of the Senate--after Sumner's "Crime Against Kansas" speech. Sumner had traveled in England and carried on regular correspondence with many political activists in Britain. Lately, he had received very worrisome letters discussing the Britsh preparations for war. (For instance, the Duchess of Argyll, herself a strong antislavery advocate, wrote Sumner that the capture of the envoys was “the maddest act that ever was done".)
Also, there was a good possibility that France would take advantage of the situation. There might be French recognition of the Confederacy and movement into Mexico and Latin America. And in fact, a message was delivered during the meeting from French Foreign Minister Thouvenel urging that the United States release the prisoners and in so doing affirm the rights of neutrals on the seas that France and the United States had repeatedly argued against Great Britain. (Nonetheless, France would invade Mexico the following year.)
Treasury Secretary Salmon Chase and Attorney General Edward Bates were strongly influenced by the various messages from Europe. Lincoln still wanted arbitration but received no support, since it would take considerable time to agree on an arbitration panel and Britain was clearly impatient. Though no decision was made at the meeting, Lincoln indicated he wished to prepare his own paper ,and a new meeting was scheduled for the next day.

Civil war? What does that mean? Is there any foreign war? Isn't every war fought between men, between brothers?
--Victor Hugo