On Friday, New York magazine's Jon Chait argued that the media has "wildly overstated the legislative importance of Republican Senate control" while at the same time understating its judicial importance. As he put it, "The contest to control the Senate is about one thing: whether Obama can confirm judges and staff his administration." A GOP Senate would spell "two years of likely gridlock," and "if a Supreme Court justice becomes incapacitated or dies, the judicial gridlock could become a Constitutional struggle." 

Chait is absolutely right—and the possibility of a constitutional crisis is all the dramatic because there's no modern precedent for it. 

The Constitution doesn't require the president to fill a Supreme Court vacancy on any particular timeline. But since World War II, vacancies on the high court have not caused partisan gridlock. The closest precedent is then-Associate Justice Abe Fortas, whom President Lyndon Johnson nominated for chief justice; a Democratic Senate filibustered Fortas over concerns about his liberal opinions and close relationship with Johnson. There were Supreme Court deaths—justices Wiley Rutledge, Fred Vinson, Robert Jackson, Frank Murphy, and, most recently, William Rehnquist—but their seats were filled in a timely manner. 

Even in the pre-WWII era, when a much higher percentage of justices died in office, vacancies were generally filled with little delay. The rejected nominees of presidents James Madison, James Buchanan, Ulysses S. Grant and others fell for a variety of quirky reasons unique to their situation, not because of gridlock; in fact, those presidents generally faced a friendly Senate. John Tyler succeeded in having only one of his six nominees confirmed, but his party also controlled the Senate.

Supreme Court nominees are especially likely to be rejected for partisan reasons at the end of a lame-duck presidency. According to the Congressional Research Service, “Opposition to the nominating President played a role in at least 16 of the 34 nominations that were not confirmed. Many of the 16 were put forward by Presidents in the last year of their presidency—seven occurred after a successor President had been elected, but before the transfer of power to the new administration.” 

As we look ahead to the post-midterm landscape, we could be in uncharted territory. Indeed, 1895 was the last time a Democratic president nominated a justice facing a Republican Senate (44 Republicans joined 40 Democrats and six senators of other parties to approve Grover Cleveland’s nomination of Rufus Peckham). Since then, every other Democratic president with a Supreme Court vacancy faced a friendly Senate.

There are, of course, several examples of the reverse dynamic, where Republican presidents faced Democratic Senates: Dwight Eisenhower, Richard Nixon, Gerald Ford, Ronald Reagan, George H. W. Bush. As we know, the nominees weren't all successful (Robert Bork) but the presidents eventually found nominees that Senate Democrats considered acceptable (Justice Anthony Kennedy).

Given the already toxic atmosphere in Congress over the politicization of the judiciary, some scholars are already predicting that Republicans will refuse to schedule hearings on President Obama’s Supreme Court nominees if they’re not “acceptable” to the GOP. 

But there’s a more optimistic possibility: Democrats can point to bipartisan Supreme Court confirmations, like justices Clarence Thomas and Antonin Scalia, where they have voted for nominees with whom they disagree. And there is next to zero historical evidence of gridlock causing extended vacancies (although that could be plausibly chalked up to the fact that we didn't experience divided government very often in the early years of the republic). Even Obama himself, in a recent interview with The New Yorker, suggested there would be pressure for Republicans to approve a nominee, saying that intense media coverage of SCOTUS nominations "means that some of the shenanigans that were taking place in terms of blocking appointments, stalling appointments [to the lower courts], I think are more difficult to pull off during a Supreme Court nomination process." 

On the other hand, there’s no particular grounds for optimism with a Democratic president and Republican Senate. With their vitriolic obstruction throughout the Obama presidency, including a fight over the debt ceiling and a government shutdown, some Senate Republicans have shown a willingness to paralyze the basic functions of government—and might be comfortable with an evenly divided Court of eight justices, which could mean repeated 4-4 deadlocks and opinions that lack precedential value. There may be a parallel in the recent drawn-out fight over the D.C. Circuit, in which Republicans accused Obama of "packing" the court—he wasn't—and were perfectly happy to leave seats unfilled. That prompted Senate Majority Leader Harry Reid to eliminate the filibuster with the nuclear option, which in turn led to Republicans promises of retaliation.

That retaliation may come at the expense of a fully functioning Supreme Court.