The position on slavery set out by Lincoln in his famous debates with Douglas formed the basis of the Republican Party's platform in the 1860 election. The GOP had been founded in 1854 with the express aim of opposing the extension of slavery into the Western territories. However, this was not the same thing as proposing the outright abolition of slavery. Lincoln realized that such a policy would sow even greater division between North and South, undermining the stability of the Union in the process.
Yet during their debates Douglas accused Lincoln of being an abolitionist, referring to his famous "House Divided" speech in which he's said the following:
I believe this government cannot endure permanently half Slave and half Free.
What Lincoln was driving at, however, was the necessity of maintaining the nation's stability as a political entity. For him, that was always the number one priority. As he said himself, he would countenance the existence of slavery in every state if it meant holding the nation together. But still Douglas persisted, hammering away at his central charge. He tried to link the abolitionist cause with racial equality, something almost no white American at the time accepted, including Lincoln. Though some of the more radical Republicans were indeed outright abolitionists, the GOP mainstream endorsed Lincoln's more cautious approach.