On April 4 when Lincoln met with a Virginian unionist he offered to evacuate Fort Sumter if Virginia adjourned their convention without secession. When the southerner didn't agree Lincoln did what he had to do. When he sent reinforcements to Fort Sumter he was simply upholding his word. If he hadn't sent the reinforcements it would have made him look weak and weakened our faith in him and the government. And anyway, the southern states don't even have the right to secede.
National sovereignty comes before state sovereignty.
Lincoln agreed with this idea. He said that without the Union there would never have been any free and independent states in the first place. Their first loyalty should be to the nation, then to their state. One other problem that has been bothering me is that lately the men and women who work in my factory have been asking for more money. I really can't afford to pay them any more money.