This text is part of a small speech in which Lincoln states that he is thankful to have been reelected during the American Civil War and illustrates the line of reasoning of his supporters by referring to a story of an old Dutch farmer. Since the argument fits the form a is X, because b is X, it can be identified as a first-order subject argument. In this specific case, a is instantiated by ‘The president in war time’, X by ‘should not be swapped’, and b by ‘horses when crossing streams’.
The president in war time (a) should not be swapped (X), because horses when crossing streams (b) should not be swapped (X)
First-order subject arguments are further differentiated by identifying the types of statement in the conclusion and the premise. In this case, they are both statements of policy, which means that we are dealing with a first-order subject argument supporting a policy with another policy (1 sub PP).
The trivial name of first-order subject arguments is derived from the characterization of the relationship between the subjects a and b. In this example, the argument draws on the comparison between the policy mentioned in the conclusion, swapping the president in war time, and the policy mentioned in the premise, swapping horses when crossing streams. We can therefore call such an argument an ‘argument by comparison’.
The example is taken from a report of Abraham Lincoln’s reply to the Delegation from the National Union League on June 9, 1864.