So when did the Supreme Court rule that he had acted unconstitutionally?
As you know, the SC ruled that a blockade -specifically- WAS constitutional. That puts me in mind of a quote:
"We are all Republicans--we are all Federalists. If there be any among us who would wish to dissolve this Union or to change its republican form, let them stand undisturbed as monuments of the safety with which error of opinion may be tolerated where reason is free to combat it."
Thomas Jefferson, March 4, 1801
Walt
That being said, I will offer you the words of the people of the time:
"Fort Sumter, situated in the entrance to the Charleston harbor in South Carolina, was held by United States troops under the command of Major Robert Anderson. A native of Kentucky, Anderson nevertheless saw his duty to the Union as paramount over his loyalty to his section of the country. However, he understood, in light of the armistice which had been entered into between South Carolina and the Buchanan Administration on 6 December 1860, that an attempt by the United States military to garrison the fort would precipitate war.
"Such was the sentiment of all but two of the seven members of Lincoln's own Cabinet. In a letter dated 15 March 1861, Lincoln asked his Cabinet whether it was wise to attempt to provision the fort, to which question his Secretary of State, William Seward, replied:
If it were possible to peaceably provision Fort Sumter, of course, I should answer that it would be both unwise and inhuman not to attempt it. But the facts of the case are known to be that the attempt must be made with the employment of military and marine force which would provoke combat and probably initiate a civil war which the Government of the United States would be committed to maintain, through all changes, to some definite conclusion....
Suppose the expedition successful, we have then a garrison in Fort Sumter that can defy assault for six months. What is it to do then? Is it to make war by opening its batteries to demolish the defenses of the Carolinians? Can it demolish them if it tries? If it cannot, what is the advantage we shall have gained? If it can, how will it check or prevent disunion? In either case, it seems to me, that we will have inaugurated a civil war by our own act, without an adequate object, after which reunion will be hopeless, at least under this Administration or in any other way than by a popular disavowal both of the war and of the Administration which unnecessarily commenced it. Fraternity is the element of union; war the very element of disunion.
But your assertion that Lincoln was not guilty of unconstitutional acts because he wasn't charged is silly. He admited, and those around him, admitted extra-constitutional actions. Lack of being charged reflects the protectionism of the republican party, not purity. So, pass this off somewhere else.