Article II, Section 1 Clause 8
"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, preserve, protect and defend the Constitution of the United States."
I think he did defend the Constitution.
Article 4 Section 4
The United States shall guarantee to every State in this Union a 1. Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence
Seems to me that after April 12 there was domestic Violence in the country. See the next paragraph.
Whereas the laws of the United States have been for some time past and now are opposed and the execution thereof obstructed in the States of South Carolina, Georgia, Alabama, Florida, Mississippi, Louisiana, and Texas by combinations too powerful to be suppressed by the ordinary course of judicial proceedings or by the powers vested in the marshals by law:
Now, therefore, I, Abraham Lincoln, President of the United States in virtue of the power in me vested by the Constitution and the laws, have thought fit to call forth, and hereby do call forth, the militia of the several States of the Union, to the aggregate number of 75,000, in order to suppress said combinations and to cause the laws to be duly executed.
I think he was trying to execute the law of the land. That was his resposibilty in my opinion. Why would the state of South Carolina expect anything less from him?
FC