Abortion continues to dominate discussion about John Roberts’s nomination and will certainly dominate commentary surrounding President Bush’s second nominee. Beyond the posturing and polemics, however, the core issue is not in play. Even if President Bush is successful in appointing two anti-abortion justices, five votes will remain on the Court to uphold Roe’s essential holding protecting a woman’s right to choose. Of more immediate consequence is the new appointees’ impact on constitutional questions that have been largely overlooked, in particular the relationship between church and state.

With Chief Justice Rehnquist’s death and Justice O’Connor’s retirement, the Court lacks a five-vote majority regarding the purpose and meaning of the First Amendment’s Establishment Clause. On cases such as posting the Ten Commandments on public property and allowing public-school children to say “under God” in the Pledge of Allegiance,” the new nominees will control future jurisprudence. As potential holders of the “swing vote,” they should be pressed about their understanding of religious freedom.

Four sitting justices–Stevens, Souter, Ginsburg, and Breyer–embrace the “wall of separation.” They interpret the First Amendment to prohibit the government from advancing one religion over others or from favoring religion generally over non-religion. In practice this creates serious doubts about religious groups participating in state-funded programs and about governmental endorsement of religion in the public square.

In 2002, for example, the four “strict-separationists” voted against allowing religious schools to participate in an Ohio school-voucher program. They argued that to allow public funds to flow to private (mostly Catholic) schools has the impermissible effect of advancing religion. The same four voted with Justice O’Connor last June to strike down Ten Commandments displays posted in two Kentucky county courthouses.

The three other remaining justices–Scalia, Kennedy, and Thomas–take a different approach. They argue that “strict-separationism” misinterprets the Constitution’s text and flatly contradicts our nation’s traditions. They interpret the Establishment Clause to prohibit “coercion” of religion–that is, compelling belief, practice, or financial support of religion. They would allow religious groups to participate in public programs like school vouchers as long as the religious groups do so on the same terms as non-religious groups. Their approach also allows non-coercive governmental acknowledgement of religion, like posting of the Ten Commandments.

The split on the Court reflects deep differences in jurisprudential philosophy, contrary understandings of the judiciary’s role, and competing assessments of the potential harmfulness of religion.

While at times paying lip service to the Founders, the more liberal justices ultimately defend the “wall” by claiming that it is the best way to prevent social strife in modern day, pluralistic America. They argue that the Court should withdraw from the normal political process questions that might divide the American public along religious lines. The implication is that the judiciary is most capable of determining how, when, and under what conditions religion may safely appear in public. And more often than not, when exercising that judgment, the “strict-separationists” vote to limit religion’s public presence because they believe it is so potentially divisive.

The more conservative justices understand their role to be more limited. They take their bearings not from what they perceive to be best for contemporary society, but rather from the Constitution’s text. What is determinative for them is that the First Amendment prohibits religious establishments and establishments, at the time of the Founding, involved coercion of religious practice by force of law and threat of penalty. They confirm this interpretation with our nation’s history, which reveals that many of the Framers who drafted the First Amendment themselves embraced non-coercive, governmental endorsement of religion. If the American people now want to allow a non-coercive religious presence in the public square, the conservative justices will not object.

From his record, we know almost nothing about John Roberts’s views on church and state. He is not going to answer questions about specific cases, but queries about judicial philosophy are fair game. Senators concerned about religious freedom should ask Roberts how he would discern the meaning of the Constitution’s prohibition of religious establishments. Would he take his bearings from the meaning of the words as they were understood at the time of the drafting and ratification of the First Amendment? Or would he follow modern day precedents that take their bearing from the judiciary’s perception of the demands of social cohesion? The same question should also be asked of Bush’s second nominee.

Before anyone assumes the awesome power of a Supreme Court justice, the American public deserves to hear responses to such questions. The meaning and extent of the Constitution’s separation of church and state, not to mention the role of the judiciary in contemporary American politics, will depend on the answers provided.

–Vincent Phillip Muñoz is assistant professor of political science at Tufts University and a fellow of the Discovery Institute.