Huckabee slanders Lincoln
Lincoln understood quite clearly that he had no power as president to free slaves legally held in the US. That is why the emancipation proclamation was done as an executive order under the exigency of war, and why it freed slaves only in the states then in rebellion. It did not even free the slaves in Tennessee, a slave state under Union forces at the time of the proclamation.
As to Dred Scott, historical writer Kevin Levin points out that Lincoln deferred clearly to the Supreme Court’s authority to decide Constitutional questions:
We think its decisions on Constitutional questions, when fully settled, should control, not only the particular cases decided, but the general policy of the country, subject to be disturbed only by amendments of the Constitution as provided in that instrument itself. More than this would be revolution.
Unlike much of what appears under his name on the internet, that really was written by Lincoln, in an article criticizing the decision. Dred Scott was not undone by Lincoln or anyone else disregarding it. It was undone by the 13th and 14th amendments to the Constitution.