A pro-abortion supreme court justice is now being appointed (singular). This justice will replace Justice Stephens, who was already pro-abortion. What did change the balance of power was the retirement of Justice O’Connor, who was generally pro-abortion. She was replaced by Justice Alito, who is more conservative on this issue. So while O’Connor was the swing vote, Justice Kennedy (who was generally a bit to the right of O’Connor in rulings on this issue) is now the swing vote, as the most liberal of the 5-justice “conservative bloc” on the court. The trouble is respect for precedent - stare decisis. While I think the five conservative justices in the absence of precedent would severely limit instances when abortion would be allowed, instead the court at this point is mostly fighting over the narrow middle ground, occasionally pushing it one way (mostly in the conservative direction in the past few years).