The Republican Party was formed to end slavery:
“The final nail in the Whig coffin was the Kansas–Nebraska Act, passed by Democrats in 1854. It was also the spark that began the Republican Party, which would take in both Whigs and Free Soilers and create an anti-slavery party that the Whigs had always resisted becoming. The Act opened Kansas Territory and Nebraska Territory to slavery and future admission as slave states, thus implicitly repealing the prohibition on slavery in territory north of 36° 30′ latitude that had been part of the Missouri Compromise. This change was viewed by anti-slavery Northerners as an aggressive, expansionist maneuver by the slave-owning South. Opponents of the Act were intensely motivated and began forming a new party. The Party began as a coalition of anti-slavery Conscience Whigs such as Zachariah Chandler and Free Soilers such as Salmon P. Chase.”
https://en.wikipedia.org/wiki/History_of_the_Republican_Party_(United_States)
Republican Abraham Lincoln was elected President....
I am aware of that. But when they got into power, they didn't try to end it through legal means, such as a constitutional amendment.
As with most lying politicians, not only did they make no effort to get rid of slavery legally, they actually voted on a constitutional amendment to make slavery permanent. It's called the "Corwin Amendment."
Republican Abraham Lincoln was elected President....
And he urged the states to pass the permanent slavery amendment known as the "Corwin Amendment."
So with all of them working to make slavery permanently legal, how anti-slavery could they be?