Editor's note: John P. Avlon is a CNN contributor and senior political columnist for The Daily Beast. He is the author of "Wingnuts: How the Lunatic Fringe is Hijacking America."
New York (CNN) -- The debate over Elena Kagan's confirmation for the Supreme Court is likely to hinge on the question of whether she is a centrist or a leftist.
It is a version of the dance that is played out with every Supreme Court nominee -- partisan supporters praise the nominee's combination of principle and pragmatism, while partisan opponents reflexively argue that his or her placement on the bench will somehow undermine the constitutional republic.
All of which begs a surprisingly little-asked question: What makes a centrist justice? Is it just the swing vote in the center of the court, or is there is a distinct philosophy behind the position?
"In constitutional adjudication, the right looks backward to the original intent of the founding fathers. The left looks beyond the Constitution to abstract ideals of human rights and social justice," says David Frum of FrumForum.com and a Harvard Law graduate. "The center you might describe as Burkean: seeking to build upon the Constitution as it is, not as it once was -- or as some might wish it would be."
Tom Goldstein of SCOTUSblog.com offers a more positional definition. "What it takes to be a centrist judge in some sense depends a lot on who is on your left and right," he tells me. "Our center justice, [Anthony] Kennedy, would have been on the right of the court 20 years ago. More broadly, centrism requires a person who doesn't have a committed ideology, who isn't necessarily with or against the government, corporations or individuals in any given case."
It is that nonideological approach to the law, and the absence of prejudgment, that causes centrist judges to function as the pivotal swing vote on the Supreme Court. They are not in the bag for the left or the right, and so they are more likely to base their decisions on the merits of a case alone. Being a centrist swing justice is a magnified version of being a centrist swing voter -- their judgment determines the winners.
Studies of so-called "median" justices -- those in the center of the court's spectrum during any given decade -- attest to the influence of the position. During the 1970s and early '80s, John F. Kennedy nominee Byron White was in the center most often, providing the winning vote in 24 out of 37 cases one year.
Nixon nominee Lewis Powell, a conservative Democrat, also cultivated a centrist reputation. "Unfailingly polite, he observed a strict code of decorum in the often rough battles on the high court, never personalizing them and always recoiling from extremes," concluded The Washington Post upon his retirement. "Powell searched for the middle ground. For this reason, experienced Supreme Court litigators often targeted Powell when formulating their arguments, believing that an argument that would suit him would inevitably attract at least four other justices."
But the archetypal Supreme Court centrist of recent decades was the first woman nominated to the court, Sandra Day O'Connor. Along with her fellow Reagan nominee Anthony Kennedy, O'Connor defined the center space of the court in recent decades, providing a modest and pragmatic balance that disappointed doctrinaire conservatives and liberals alike. "From her rural childhood to her career climb through a profession dominated by men, O'Connor often resorted to practical solutions as she worked within the system. This tendency to moderate, in turn, enhanced her importance in an often-splintered Court," according to the Oyez Project, a website about the court. "Her moderation has helped her role as the centrist coalition-builder, which has consequently enhanced her influence on the Court."
The key question in divining Kagan's potential position and impact on the court is her ability to be just such a coalition builder. Absent a record as a judge, Kagan's time as Obama's solicitor general, the dean of Harvard Law School and an aide to President Clinton are the essential indicators. Memos from Kagan's time as a legal and policy adviser in the Clinton White House show her to be driven by political pragmatism more than ideology.
Her social liberalism and Democratic Party background are balanced by an expansive belief in executive power, which has pleased advocates for an assertive war on terror but troubled civil libertarians. And she enjoys the personal support of leaders in the conservative legal community, ranging from Reagan Solicitor General Charles Fried, Clinton special prosecutor Kenneth Starr, George W. Bush Solicitor General Ted Olson and blocked Bush judicial nominee Miguel Estrada. That last point, at least, shows a talent for coalition building that could bode well for her influence on the center of the court, if confirmed.
Kagan might be best described as a center-left pragmatist, qualities that she shares with the president who nominated her. She is unlikely to be as liberal as Justice John Paul Stevens, the liberal Republican nominated by Gerald Ford, whom she is replacing -- and the court's balance, dominated by conservatives, is not likely to shift to the left.
Despite her surprising support from some conservative legal scholars -- and opposition among some liberal court commentators -- most senators at her confirmation can be depended on to parrot the old harshly partisan narratives.
In so doing, they will miss the larger lessons of recent court history -- the center is where the action and influence is, not the left or right. The reality is that life does not conform to easy ideological labels and neither should a Supreme Court justice.
The opinions expressed in this commentary are solely those of John P. Avlon.