O'Connor is the swing vote, the one favoring compromise. Replacing Rehnquist and Stevens will seal for a generation, what Bush achieves by replacing O'Connor. Since FDR's court-packing scheme panicked the gilded Age SCOTUS in letting the New Deal go forward, liberalism (leftism) has depended on the court to confirm and support liberal progress (left agenda) as a matter of idealistic principle.
This person just made the argument that the only way leftists can forward thier agenda is thru the courts because they can't win legislative or executive victories. This disproves the claim that there are no "activist judges".