The yawning ideological gap between pivotal senators and President Barack Obama will prevent Supreme Court Justice Antonin Scalia’s vacant seat from being filled quickly or easily.

Yesterday I suggested ways in which the president can maximize his chances of making an appointment in the face of this constraint: Nominate a well-qualified individual with a squeaky clean background and lobby vigorously for that person. Still, the increasingly partisan and ideological nature of the confirmation process means that an obvious ideologue with a sterling résumé will still struggle to be confirmed (see: Bork, Robert).

So what should Obama do? We know the president is resolved to try to make an appointment. Further, he obviously wants a justice who will shift the swing vote of the Supreme Court in a liberal direction. How can Obama balance the competing demands of securing confirmation and appointing a reliably liberal justice?

My research uncovered two regularities of modern Supreme Court appointments.1 First, nominees with more experience as federal appellate judges and/or in the administration of their appointing president are more congruent with their appointing president.

Using Michael Bailey’s excellent data, we can compare the ideology of Supreme Court justices with that of their appointing presidents, as shown in the figure below.2 Clarence Thomas’s votes, on average, are the most congruent with his appointing president’s preferences. David Souter’s votes are, on average, the least congruent. Highlighted in red are justices with two years or less of experience in either the federal appellate courts and/or in the administration of their appointing president.3

The second regularity of appointments is that justices confirmed when the president is constrained by a hostile Senate have less such experience.

At times, presidents nominate less experienced individuals when they anticipate fierce resistance — the infamous “stealth candidate.” It’s possible that without a lengthy record to attack, senators and interest groups will struggle to mobilize opposition to such a nominee. As the chart shows, stealth candidates come with their own risks for the presidents who nominate them.

Ultimately, here’s what Obama’s best realistic shot at appointing a liberal justice to Scalia’s seat might look like: Nominate a well-educated, scandal-free, lesser-known commodity and lobby vigorously for that nominee to the public. It’s a risky strategy, but it probably beats appointing Orrin Hatch. And even that best realistic shot may not be enough to secure confirmation in today’s Washington.

Matthew P. Hitt is an assistant professor of political science at Louisiana State University, specializing in American political institutions and public law.

Senate Majority Leader Mitch McConnell recently made a public vow to prevent President Obama from appointing Justice Antonin Scalia’s replacement. The reason for this stance is obvious. With Scalia on the Court, the median justice (read: swing vote) in the previously completed term was Justice Anthony Kennedy, as shown in the figure below. Therefore, if Obama appoints anyone to Kennedy’s left, the new median would be either that person or Justice Stephen Breyer (if the nominee is to Breyer’s left).

Based on the data of Martin and Quinn (2002), see here for details and the original papers.

Conversely, anyone desirable to McConnell would have to be equivalent or to the right of Kennedy. It’s hard to imagine Obama choosing such a person. Sophisticated theoretical models based on this intuition generally predict that anyone the president nominates in this situation will likely be rejected*. So it’s gridlock again, right?

Not so fast, my friend. New research — some forthcoming, some in progress — shows that presidents have been more successful in getting their nominees confirmed than these widely utilized theories predict. Why? For starters, these theories assume there are no penalties for obstruction. In fact, Republican senators up for reelection will need to decide whether it’s riskier to defect from their party or obstruct the president; either choice seem likely to bring either primary or general election costs, respectively.

The president might be able to affect this decision. Research shows that in general, the more public statements a president makes in favor of a nominee, the more “yes” votes that nominee receives. Obama will likely try to overcome the gridlock by lobbying the public, hoping to intensify pressure on Republican senators.

Will this lobbying work? It probably depends on the nominee. Since 1950, six Supreme Court nominees were either rejected by the Senate or withdrawn by the president. In five of the six cases, poor nominee qualifications, together with ideological concerns, arguably played a significant role in their failure. The table below shows these nominees, along with their non-ideological reason for failure. This history suggests a nominee with dubious qualifications or ethical issues will struggle to gain traction in the face of a hostile Senate.

Bottom line: Obama probably cannot nominate someone who shares his ideology closely, given the preferences of Republican leaders in the Senate. Yet research and history tell us the president can succeed by nominating a well-qualified individual with a skeleton-free closet, and by lobbying fiercely on that nominee’s behalf. The failure of Robert Bork also suggests that the president should avoid a nominee with a lengthy record of extremism, even if that nominee is exceptionally qualified.

Table 1. Failed Supreme Court nominees, 1968-2005

See also Neubauer and Meinhold (2007, 484). Homer Thornberry is omitted; his nomination became moot after Fortas’s nomination for chief justice was withdrawn.

Given these dynamics, how can President Obama maximize the likelihood that his nominee actually ends up voting as a reliably liberal justice once on the Court? I’ll address that in part 2, in which I discuss the congruence between presidents and the justices they appoint.

*A less extreme version of this argument is that the Court’s median will not change much as a result of an appointment in such a contentious situation; see Krehbiel (2007).

**G. Harrold Carswell deserves special mention here. Upon charges that he was a “mediocre” nominee in terms of professional qualifications, Sen. Roman Hruska (R-NE) argued, “Even if he is mediocre, there are a lot of mediocre judges and people and lawyers. They are entitled to a little representation, aren’t they, and a little chance?”

Matthew P. Hitt is an assistant professor of political science at Louisiana State University, specializing in American political institutions and public law.