The fight over Justice Antonin Scalia's successor on the Supreme Court is going to be massively more politicized than any nomination fight we've seen in decades. It may even be the most acrimonious and high-stakes nomination fight ever.

For the past quarter-century, the Court has been narrowly divided between five conservatives and four liberals. The close split has produced a long series of decisions in which a five-justice majority adopted conservative interpretations of the law over the objections of the court's four liberals.

On Saturday, Scalia, the court's most venerable conservative, died, putting the high court's ideological makeup up for grabs for the first time in decades.

A political fight erupted within hours of the news of Scalia's death, with Senate Majority Leader Mitch McConnell echoing his fellow Republicans in all but promising to block whomever President Barack Obama nominates. Democrats are already demanding the Senate approve whoever Obama proposes (even before knowing who the candidate is).

If the Senate doesn't confirm Obama's nominee — and it seems pretty likely that it won't — that will raise the stakes in what was already shaping up to be a monumental presidential race. The next president will not only get to run the country for four years, he or she could define the ideological balance of the Supreme Court and reshape US law for a generation.

This is about to get ugly

When a Supreme Court justice dies or retires, the president has the right to appoint a successor subject to Senate confirmation. Until the 1980s, the president's appointees were usually approved with little controversy. But in the past couple of decades, nomination fights have been increasingly controversial and partisan. The last three people to join the Supreme Court — Bush nominee Samuel Alito and Obama nominees Sonia Sotomayor and Elena Kagan — all had more than 30 senators vote against them.

And this time, the situation is likely to be far more intense and far more partisan for several reasons.

First, we'll have a Democratic president, Barack Obama, choosing a successor for one of the most conservative justices on the Supreme Court. Generally, this is not how it happens. Recent nominations have all occurred early in a president's term, largely because liberal justices tend to resign at the start of a Democratic presidency and conservative justices tend to resign at the start of a Republican presidency, thereby maximizing the chances that a like-minded president will be able to appoint their successor.

Second, the Senate is controlled by the Republicans — 54 to 46. Democrats would need to stand together and convince at least four Republicans to join them. That is a tall order. Republicans can be expected to have little interest in supporting Obama's nominee. Recent resignations (and the death of Chief Justice William Rehnquist in 2005) have all occurred when the Senate and the president were held by the same party.

Finally, Obama has less than a year left in office, making it plausible that the Senate could run out the clock in the hopes that a Republican wins the White House. McConnell already more or less promised this strategy in a release he sent out just hours after Scalia's death.

Liberals will demand quick confirmation. Conservatives will call for patience.

The outlines of the coming debate began to emerge just hours after news of Scalia's death broke. Conservatives such as Ted Cruz (R-TX) are arguing that the Senate should refuse to confirm Obama's nominee to give the next president the opportunity to do so. Liberals such as Sen. Patrick Leahy (D-VT) are calling for the Senate to swiftly confirm Obama's nominee.

Liberals are pointing out that Obama still has 11 months left in his term, and arguing that it would be unprecedented for the Senate to hold up a Supreme Court nomination for that long. Many people on Twitter are pointing to a tweet from a historian stating that the Senate has never taken longer than 125 days to decide on a nominee (more details here), compared with 342 days remaining in Obama's term. But others have pointed out that it took two years to replace a Supreme Court justice who left the bench in 1844.

Liberals also point out that Justice Anthony Kennedy, who currently holds the court's swing vote, was confirmed easily by the Senate in 1988, the last full year of Ronald Reagan's presidency. Conservatives, however, note that Kennedy was actually appointed in 1987 — and only after Democrats rejected the more conservative Robert Bork for the seat.

Regardless, conservatives will argue that this time is different. The country and the Supreme Court are more polarized than they've been in decades, and because the Supreme Court is evenly divided, Scalia's replacement will have unprecedented power to reshape the law on everything from abortion to campaign finance. They'll argue that the voters should have the opportunity to decide, via the presidential election, whether the Supreme Court should have a liberal or conservative majority.

And regardless of what you might think about these arguments, the hard reality for Democrats is that the Senate has a 54-46 Republican majority and a Republican majority leader, Mitch McConnell.

We can expect grassroots conservatives to put intense pressure on McConnell and other Republicans not to confirm whomever Obama nominates. Given the stakes, and the success conservatives have had in mounting primary challenges against moderate Republicans who stray from conservative positions, it's going to be a big challenge for Obama to convince McConnell to bring up his nominee for a vote, or to convince at least four Republicans to vote for his nominee.

An open Supreme Court seat would be a huge campaign issue

If Justice Scalia's seat is still open in November, it's going to loom as one of the biggest issues in an election that was already shaping up to be hugely consequential. A president serves for just four years before having to face the voters again. Supreme Court justices serve for life, and because they tend to resign when there's a like-minded president in office, control over a seat by liberals or conservatives could easily last longer than the term of any single justice.

So an open seat would mean that the 2016 election wouldn't just determine whether the Supreme Court has a liberal or conservative majority in 2017 — it could determine the ideological composition of the Supreme Court for decades to come.

Electing Hillary Clinton or Bernie Sanders would allow them to replace not only Scalia but possibly liberal Justices Stephen Breyer and Ruth Bader Ginsburg, giving the Court a liberal majority well into the 2030s. Conversely, President Ted Cruz could replace not only Scalia but also conservative Justice Anthony Kennedy with a more conservative jurist, strengthening the Court's conservative majority for a long time to come.