During the Supreme Court confirmation process last year for Sonia Sotomayor, NationalJournal.com created a series of graphics based on data compiled by Lee Epstein of Northwestern University and her colleagues, along with Jeffrey Segal of Stony Brook University. Examining this data again in the context of Justice John Paul Stevens' retirement sheds light on what's at stake for President Obama and conservatives in the coming confirmation fight -- and may provide some clues as to who the nominee will be.

Ideology

In Jeffrey Segal's analysis of nomination news coverage, Justice Stevens ranked as the 12th most conservative nominee since the FDR era as perceived by media accounts -- ahead of several other Republican court picks, including Reagan nominees Sandra Day O'Connor and Anthony Kennedy. (On the chart below, 0.0 indicates most conservative and 1.0 most liberal.)

The fact that Stevens was seen as a conservative nominee and yet is now considered the court's leading liberal is evidence of what Segal says has been a rightward drift among nominees. The following chart traces nominee ideology over time:

Stevens has said that he's remained true to his conservative values over the years while the court has moved far to the right. Yet many court observers have argued the opposite, suggesting that Stevens is one of many Republican nominees who have become more liberal once safely on the bench. This is the basis for the longstanding conservative argument that the court's movement over time has in fact been leftward.

These two conflicting arguments have intensified the confirmation debates in recent decades, and will put pressure on both President Obama and Senate Republicans to counter the perceived ideological trend by any means necessary.

Longevity

Stevens was only two years away from the all-time record for longevity on the court, part of another trend identified in our analysis: that GOP nominees have served five years longer on average than Democratic nominees.

Of course, Stevens is one Republican nominee whom conservatives wish had retired much earlier. As the court has become increasingly politicized, longevity has become more important, and President Obama has to contend with the likelihood that the relatively youthful George W. Bush nominees, John Roberts and Samuel Alito, will be a force on the court for a generation. Age is one of the main reasons that many observers believe 49-year-old Solicitor General Elena Kagan is the real front-runner, as opposed to appellate court judges Merrick Garland and Diane Wood, who are both nearing 60.

Experience

Stevens came to the court with only five years of federal bench experience, which was about the norm at the time. The more recent trend has been to nominate more experienced federal judges, as the following chart demonstrates:

Since the court is now stocked with experienced federal judges, some have called on Obama to reverse this trend and look to nominees with a wider range of experiences -- Kagan, Secretary of State Hillary Rodham Clinton, Homeland Security Secretary Janet Napolitano, Sen. Amy Klobuchar, D-Minn., or Cass Sunstein of the Office of Information and Regulatory Affairs.

Interested Observers

Segal also tracked interest group activity during the nomination process and found a sharp uptick in activity surrounding the Sotomayor nomination last year, with more than 200 groups submitting testimony in support of the first Latina nominee.

Since the next nominee is unlikely to make history as Sotomayor did, the participation from liberal interest groups figures to be lower this time around. But conservative groups seem to be preparing for an aggressive assault on the nominee, fired up not only by the perennial ideological battles but also by anger over the president's policies and excitement over the upcoming midterms.