IMAGINING THE NEXT CONFIRMATION FIGHT…. It’s funny to think about it now, soon after Justice John Paul Stevens announced his retirement, the conventional wisdom was that Elena Kagan was the kind of nominee even Republicans could accept. Indeed, some of the strongest criticism of Kagan was coming from the left, not the right.

As we saw yesterday, she ended up with 63 confirmation votes in the Senate, including only five out of 41 GOP members. Historically, that’s pretty low, especially give how uncontroversial Kagan’s nomination was. Republican opposition was based on largely nothing.

Whether President Obama will have another opportunity to fill a high court vacancy is unclear, but the trend in the Senate isn’t encouraging. Ruth Bader Ginsburg had been head of the ACLU’s Women’s Rights Project, and she garnered 96 votes in Clinton’s first term. Now, Kagan could only muster 63 votes, and Republicans didn’t lay a glove on her.

“We are well on our way to a huge train wreck,” veteran Supreme Court litigator Tom Goldstein said. “I do think this is a corner we won’t be able to turn back [from], or at least there’s no sign the Senate will turn back from, for a long time.” If 60 “yes” votes “is the best anyone is going to have, a Supreme Court confirmation fight could easily turn into thermonuclear war.”

Jay Bookman added that yesterday’s vote was “an ominous sign, confirming a sense that American government is coming close to a breakdown.”

Of course, all of this dealt with a center-left justice being replaced with another center-left justice under a center-left president. Jeff Greenfield recently considered what would happen if Obama had a chance to replace one of the Supreme Court’s five conservatives.

[I]magine it’s 2011, and the Senate has become more Republican than it is now; And imagine that Clarence Thomas or Antonin Scalia — or Roberts or Alito or even Anthony Kennedy (the “swing justice”) — has to leave the bench.

For conservatives, anyone likely to be picked by President Obama’s will represent a dramatic shift on the Court. Why? Because many of the Court’s recent controversial decisions — on gun rights, late-term abortions, corporate campaign spending — were 5-4 votes. The impact of an Obama-chosen justice replacing a conservative on the Court would be far, far more consequential than Sotomayor for Souter or Kagan for Stevens.

And that means that the confirmation struggle is likely to go “nuclear.”

Given what we’ve seen, it seems to be a mortal lock that Republicans would filibuster any Obama nominee chosen to replace a conservative. In fact, I suspect the GOP would be satisfied to simply allow the Supreme Court to just go with eight justices indefinitely.

And the fact that this seems entirely plausible is a reminder of how far Republicans have moved in a short period of time. As we talked about yesterday, just two years ago, John McCain noted, “When President Bill Clinton nominated Stephen Breyer and Ruth Bader Ginsberg to serve on the high court, I voted for their confirmation, as did all but a few of my fellow Republicans. Why? For the simple reason that the nominees were qualified, and it would have been petty, and partisan, and disingenuous to insist otherwise. Those nominees represented the considered judgment of the president of the United States. And under our Constitution, it is the president’s call to make.”

The GOP simply doesn’t believe this anymore. Sen. Lindsay Graham (R-S.C.), who backed Kagan yesterday and Sotomayor last year, said, “Things are changing. I worry the direction we’re drifting.”

He’s not the only one.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.