The Court’s balance of power changes one death at a time, as we’ve all been reminded by the passing of Supreme Court Justice Antonin Scalia. In recent times, Supreme Court justices have timed their retirements to allow a president with similar politics to fill their seat, so that ideological change on the Court occurs slowly and largely by chance.

Remarkably, Republican presidents over the postwar period squandered several opportunities to transform the Court. As a result, the Court has polarized more slowly than in Congress or nationwide. That helps to explain Republicans’ expected refusal to consider any Obama nominee short of a Scalia clone.

This is the first time a president has the chance to transform the Court in a period in which Court polarization is at an all-time high. Confirming an Obama-preferred liberal nominee today would give us the first ideologically homogeneous majority since Earl Warren led the Court a half-century ago.

Republicans missed opportunities to stack the Court ideologically

As I show in “American Gridlock” (Chapter 8), presidents from Harry Truman to George H.W. Bush failed to consistently appoint reliable ideologues to the Court, for two reasons: because they frequently did not put ideology first, and because they often faced divided government. Despite having made 12 out of the last 16 appointments, Republican presidents missed many opportunities to transform the Court.

As a result, a majority coalition of reliable conservatives never coalesced — despite the GOP’s frequent control of the White House. From Nixon to George H.W. Bush, Republican presidents made 10 straight appointments, six of which could have replaced liberals with reliable conservatives. But not all did.

The chart below shows the consequences of GOP presidents’ appointments. In “American Gridlock,” I analyze justices’ tendencies to join liberal and conservative majority opinions. Based on that research, justices serving between 1946 and 2013 are designated as reliable ideologues or swing voters. The chart displays select Courts from the late 1960s to the present. We can easily see three trends.

First, several Republican appointees became key swing justices, which gave the Court a robust center (particularly between 1975 and 1981). That meant that the Court became polarized more slowly than Congress did over the same period.

Second, this era witnessed liberal conversions by Republican-appointed Justices Blackmun, Stevens and Souter. That balanced liberal and conservative poles.

Third, the Court did not reach its greatest level of polarization until 2006. Although the political center of the Court has shrunk over time, Justice Anthony Kennedy’s swing votes have limited Court polarization. To be sure, the Court has gotten more ideologically polarized, but more slowly than perhaps expected.

In response to six consecutive strategic retirements, the likes of which were more rare before the 1990s, Presidents Clinton, George W. Bush and Obama chose nominees who were ideologically compatible and reliably so. During all six of these nominations, the president’s party also controlled the Senate.

That’s what solidified liberal and conservative coalitions, “sorted” the Court by party for the first time in 2010, and produced the most polarized Court in history.

This battle has been coming for a while — and it’s a big one

The death of an ideologically reliable conservative while a liberal president is serving means this appointment has higher stakes than most. It comes in a new era of contentious nomination battles, as liberals and conservatives scramble to transform the Court or prevent the other side from doing so.

Senate Republicans say they will block consideration of a late-term nomination from Obama. Certainly the GOP Senate will likely hold up any nominee that moves the Court even slightly to the left — i.e., anyone to Justice Kennedy’s left. Any moderate or center-right justice similar to Kennedy will also face intense scrutiny because it would mark a return to the 1994-2005 Court where there were two swing justices—O’Connor and Kennedy. Those years were not kind to conservatives; 57 percent of highly salient rulings broke in the liberal direction.

Senate Republicans aim to wait until a new president takes office in 2017. If the new president in 2017 is a Democrat, we will still have the “perfect storm” scenario. That’s a bit of a gamble for Republicans, as a new president might have more political capital to expend on a nominee.

If Democrats gain the White House this November, perhaps Republicans would work with President Obama on a consensus pick in a lame-duck session, ceding as little ideological ground as possible on the Court. But Obama could say “no thank you” and let his Democratic successor get someone better.

Absent a Democratic filibuster, a Republican presidential appointment in 2017 would be far less contentious, since a conservative nominee would not change the ideological balance of power on the Court. A Democratic filibuster, however, could incite Republicans to go nuclear — banning filibusters of Supreme Court appointments.

In other words, no matter who wins the election, the nomination could be even more combustible next year.

Brandon L. Bartels is an associate professor and the director of graduate studies in the department of political science at George Washington University.