1. Buchanan would not have attempted to stop it, because he did not the power.
2. Lincoln would not have attacked because of the quarrel will have been or may be considered by him as past.
There are many interesting things in this article. Below is the proof I've been looking for and is very important to me and the Fort Sumter/Fort Pickens story...
Blair ADMITS that President Lincoln foiled the attempt at supplying Fort Sumter by secretly "surreptitously withdrew from the expedition the vessel chiefly relied on to effect the relief, and thus foiled the attempt." The ship of course was the screw steamer USS Pocahontas, 4 X 32 pounders, 1 X 10 pounder, 1 X 20 pounder Parrott rifle.
The Magazine is...
The United Service, A Monthly Review of Military and Naval Affairs, Vol. VI, Third Series, Page 21. 1904.