How would the early Republican Party have felt about the Dred Scott decision?
It pushed the new Republican Party from its Free-Soil roots into becoming the party of abolitionists.
The Republican Party has gone through some identity changes over the years--It's certainly going through one right now--but in its original form, it was created to oppose the spread of slavery into the new territories. It was founded in 1854 from the remaining elements of the Whig and Free-Soil parties.
The earliest Republicans were not, strictly speaking, abolitionists. They opposed the practice of slavery on moral grounds but acknowledged that the Constitution permitted slavery in the states where it was legal. Their aim was to prevent the practice from expanding into new states and territories, specifically those gained in the then-recent Mexican War. Abolitionists were associated in the public mind with John Brown, a violent radical, and the Republicans wanted to present themselves as responsible moderates.
The Dred Scott decision, from 1857, concerned a somewhat different legal issue: could a slave who had set foot in a free state assert his own freedom, even if he went back to a slave state? The Supreme Court ruled that he could not. People of African ancestry, even in free states (Scott had spent four years in Illinois and the Wisconsin territory) were not considered American citizens and had no standing to bring the issue to trial.
The Court had hoped that giving a final word to an increasingly divisive issue would allow Americans to put the matter behind them and move on, but that was not what happened. This was one of the issues that pushed moderate Republicans into becoming full-on abolitionists.