Justice Scalia's death on Sunday marks the first time since the late 1980s, when I was in high school, that there has not been a moderately conservative majority on the U.S. Supreme Court.
President Obama will nominate someone to fill this post, whom the U.S. Senate may or may not confirm, and may make a vacancy appointment to the post if he is given an opportunity to do so (although a recent U.S. Supreme Court decision in a case involving the NLRB leaves the Republican controlled Senate a clear roadmap to prevent that from happening).
The U.S. Senate has not abolished the filibuster for U.S. Supreme Court appointments (although there is now precedent to allow it to do so by majority vote) and a majority vote is required to confirm an appointment, so a Republican controlled Senate could refuse to approve an Obama nominee even in a vote on the merits of the nomination (that they might feel politically compelled to hold). The Republican controlled U.S. Senate probably would refuse to do so if the nominee was viewed as an unabashed liberal.
But, given the reality that the next President could be Bernie Sanders or Hillary Rodham Clinton, and indeed, is more likely to be a Democrat than a Republican, and given the reality that there is a realistic chance that the Democrats will retake the U.S. Senate in the 2016 election, filibustering a moderately liberal Obama nominee to the U.S. Supreme Court might not be a wise choice for Senate Republicans worried about how much a U.S. Supreme Court appointment could shift the court's jurisprudence.
In the meantime, a U.S. Supreme Court divided 4-4 will affirm the U.S. Court of Appeals or state supreme court ruling appealed in all cases that would have resulted in a 5-4 conservative reversal, while almost all cases that would have resulted in a 5-4 liberal ruling will generally result in a 5-3 liberal ruling now, since Justice Scalia was rarely a swing vote in 5-4 decisions decided on partisan lines. Even in cases where a conservative majority would have voted 5-4 to affirm a conservative decision below, a 4-4 ruling leaving that decision in place will prevent a ruling applicable only in one circuit or only applicable in one state from having national applicability in all courts.
And, as many observers have noted, the U.S. Court of Appeals has a liberal majority in most circuits as a result of seven years of intermediate federal appellate court appointments by President Obama. So, the U.S. Supreme Court more often reverses federal appellate court decisions in a conservative direction than a liberal direction.
The restoration of a liberal majority on the U.S. Supreme Court after more than a quarter of a century could profoundly chance the character of American jurisprudence (for the better). And, if a Democrat wins the Presidency in November, further appointments could cement this liberal majority for a long time.