Whoa! Hold back on that high horse.
Remember, twice as president Lincoln took an oath to defend and preserve the pro-slavery United States Constitution.
If you want to you can argue Lincoln wasn't serious about upholding the pro-slavery United States Constitution and that, if fact, he did everything he could to destroy the Constitution. There is much evidence to support that argument.
The 13th amendment banning slavery was not ratified until Dec of 1865. The union states of Missouri, Delaware, Kentucky and Maryland were all slave states. Slavery, prior to the passage of the 13th amendment forbidding chattel slavery was a 10th amendment option of the individual states. The US constitution did not REQUIRE it, even though the Fugitive Slave Clause did allow for the interstate apprehension and return of runaway slaves.
Given the constitutional realities of the time, Lincoln had NO constitutional authority to interfere with slavery in those slave states not in rebellion against the US. The Emancipation Proclamation was an executive order aimed at depriving the Confederacy of the military utility of the labor of their slave population, and was framed as such.
Lincoln can hardly be blamed for a constitution that at the time did not allow for him to end the evil institution of slavery, anymore that Trump should be blamed for not being able to end the horror of unchecked in the womb baby slaughter of innocent infants in those states supporting abortion.
There are other grounds to accuse Lincoln of constitutional infidelity, but his position on slavery is not one of them.