Answer:
Sentence C supports best the idea.
Step-by-step explanation:
In sentence C, the author pointing out at the fact that the nomination of Amy Coney Barrett would swing the Supreme Court conservative, because conservative justices would now have a clear numerical advantage.
The prospect is then, according to the author, that issues related to heathcare and abortion could reach the Court again, and that decisions related to these issues, could be taken under a conservative bias.