He was vicepresident of the United States from 1845 to 1849, but the appointment of Buchanan as secretary of state at once shut him off from all hope of party patronage or influence in the Polk administration, and he came to be looked upon as the leader of that body of conservative Democrats of the North, who, while they themselves chafed at the domination of southern leaders, were disposed to disparage all anti-slavery agitation.
For several years after his retirement from office, he devoted himself to his law practice, and in 1856 succeeded James Buchanan as United States minister to England, where he remained until relieved by Charles Francis Adams in May 1861.
In the election of 1860 he voted for the fusion ticket in New York which was opposed to Abraham Lincoln, but he could not approve of President Buchanan's course in dealing with secession, and later supported Lincoln.
The addition of some of the liquid squeezed out from a blood-clot, of the squeezed blood-clot itself, or of a little blood-serum, is sufficient to throw down a fibrinous coagulum (Buchanan), evidently by these substances supplying the fibrin-ferment.
While directing a fire of hot shot to burn the "Congress," Commodore Buchanan of the "Merrimac" was severely wounded and was succeeded in the command by Lieutenant Catesby ap Roger Jones.
