Lincoln certainly did not waffle on the question of whether it’s constitutionally permissible for states to abandon the union. But some rednecks (and I say to all rednecks: be proud of that neck) and Southrons [sic] even yet beg to disagree with what went down. The fact that chattel slavery based on kidnapped slaves and racial bigotry was heavily tied up in the economies of a lot of the South doesn’t make them look all that good (and I would wholeheartedly agree with theologians who aver that the South was cruising for a divine bruising on that matter and that the Civil War was probably it), but Lincoln being less than totally altruistic didn’t free the Northern slaves together with the Southern ones but waited. It is a checkered history. Still, it’s sad that the Republican party in the Land of Lincoln is a faint shadow of its old idealistic self.
But he did try to promote a plan of compensated emancipation in the Union slave states which was rejected.
Lincoln had no Constitutional power to free slaves in states that were not in Rebellion. If he had tried that, the Courts would have promptly overruled his order.
As CiC of the armed forces, however, he did have the power to seize enemy property and dispose of that property as he saw fit (i.e. free the slaves) in rebellious areas that came under control of the Union Army.
And if you check the history, he did end slavery in the District of Columbia (Federal Territory) and he repeatably implored the Union states that allowed slavery, (KY, MD, DE, & MO) to end slavery on those states. Missouri and Maryland did before the end of the war. The 13th Amendment, which Lincoln pushed through congress, ended it everywhere else.