The Senate, in all its august wisdom, used to approach nominations to the Supreme Court with a simple standard: If the nominee was qualified and wasn’t a criminal or a drunk, he or she would probably get confirmed with the support of both the president’s party and the opposition. There were exceptions over the years, but most justices got the affirmative votes of even senators who didn’t agree with their political philosophy.

But we may have entered an era with an entirely different starting presumption: not that a well-qualified nominee deserves confirmation, but that senators ought to oppose any nomination from a president of the other party. The consequences could be dire, not just for the vacancy the Court is currently experiencing because of the death of Antonin Scalia, but for the Court’s future and the next presidency. Republicans are all in agreement that they should refuse to allow Barack Obama to fill Scalia’s seat, on the grounds that he’s Barack Obama. But they could well refuse to fill the seat even for the next president.

To understand where we’ve come to, let’s look at the confirmation votes of the current justices and Scalia:

  • Antonin Scalia (1986): 98-0
  • Anthony Kennedy (1987): 97-0
  • Clarence Thomas (1991): 52-48
  • Ruth Bader Ginsburg (1993): 96-3
  • Stephen Breyer (1994): 87-9
  • John Roberts (2005): 78-22, 20 of 42 Democrats in favor
  • Samuel Alito (2005): 58-42, 4 of 45 Democrats in favor
  • Sonia Sotomayor (2009): 68-31, 9 of 40 Republicans in favor
  • Elena Kagan (2010): 63-37, 5 of 40 Republicans in favor

Clarence Thomas’ confirmation was a unique case, with credible allegations of sexual harassment. But him aside, what we see is that through the Clinton administration, justices got near-unanimous votes. Then things changed starting with the George W. Bush administration. While Democrats did their best to find some dirt on John Roberts and Samuel Alito and Republicans did the same to Sonia Sotomayor and Elena Kagan, none of it amounted to much of anything. Yet in all those cases, most of the opposition party voted against the nominee.

And it’s likely to get even worse.

To see why, let’s look at Kagan’s nomination. Kagan was perfectly well-qualified (a former dean of Harvard Law School and Solicitor General), had no absurd legal views, and never shot a man in Reno just to watch him die. Nevertheless, only five Republicans voted to confirm her. Three of those senators — Richard Lugar, Olympia Snowe, and Judd Gregg — were moderates who are no longer in the Senate. The other two, Lindsey Graham and Susan Collins, might vote for a future Democratic nominee (they both voted to confirm Sotomayor as well), but they’re likely to be the only ones. That’s because the Republican Party keeps moving to the right, and just as in the House, most GOP senators now probably consider a primary challenge the greatest threat to their job. Anyone who voted to confirm any Democratic nominee would become a target for conservatives everywhere.

But in the last four confirmations, it didn’t matter that the votes were partisan, because the Senate happened to be controlled by the president’s party. Now consider this scenario. Republicans could hold out and refuse to even hear the nominee President Obama puts up for Scalia’s seat, no matter how much political damage it does them (and it will be ample, though that’s a topic for another time). Then let’s say Hillary Clinton is elected and immediately sends up a new nominee (or maybe the same one). That nominee will presumably get a hearing and eventually a vote. But let’s further imagine that though Clinton is the president, Republicans have held on to a majority in the Senate, which they well might. Will there be more than one or two who would vote for Clinton’s nominee and swing the Court to the left?

The question is particularly volatile because this is the first time since Clarence Thomas replaced Thurgood Marshall in 1991 that the ideological balance on the Court will actually change. In the six prior cases, from Ginsberg through Kagan, either a Republican president filled the seat of a conservative justice or a Democratic president filled the seat of a liberal justice. Now the stakes are even higher, both substantively and politically. Every Republican senator trying to decide what to do will know that if they vote to confirm any Democratic nominee for this seat, a primary challenge from the right will probably be in the offing the next time they run for re-election.

While there might be a slightly different calculation in a case where a Democratic president was appointing a replacement for a liberal justice, even then it’s hard to imagine more than one or two Republicans voting to confirm. If they still hold a majority in the Senate, it could mean that no justice could be confirmed until there’s a Republican president. You could imagine the Court going down from nine members to eight, to seven, and maybe even smaller.

If that sounds unlikely, then you might want to familiarize yourself with today’s Republican Party. They haven’t just grown more ideologically conservative in recent years, they’ve also grown more procedurally radical. Again and again, they’ve decided that the system of formal and informal norms that make the government work can be discarded if it becomes inconvenient. Shut down the government? You bet! Filibuster every bill more consequential than the naming of National Earwax Awareness Week? Sure! Bring America to the brink of defaulting on its debt? Why not! And every incentive Republican members of Congress have pushes them to be more uncompromising, more reckless, and more pure in their opposition to anything and everything any Democrat wants.

We could reach a similar stalemate in the case of a Republican president trying to get a nominee past a Democratic-controlled Senate, but at least in the short term, that’s a far less likely scenario than a Democratic president facing a Republican Senate. Everyone now understands that the Supreme Court may be the most important issue in this election (which I’ve been arguing for some time), not only because of this vacancy but because of the advanced age of so many of the justices. That means that the next president could get to fill two, three, or even four seats. Or maybe she won’t get to fill any at all.