One of the most momentous and least-discussed topics in the presidential campaign is the likely departure in the next four years of as many as three of the more liberal justices on a closely divided U.S. Supreme Court.
When the subject of judicial appointments was raised during Wednesday's debate, Democrat Barack Obama observed that Roe vs. Wade, the 1973 Supreme Court ruling that legalized abortion, "probably hangs in the balance" on the outcome of the election.
Obama, who supports the ruling, and Republican John McCain, who wants it overturned, then took pains to deny that they would use the case as a "litmus test" in choosing a future justice - denials that their own words appear to contradict.
As McCain put it, he doesn't believe anyone who backs Roe vs. Wade "would be part of those qualifications" he will require for judicial nominees, such as "a history of strict adherence to the Constitution." Obama, for his part, has said he favors nominees who support the constitutional right of privacy, the legal underpinning of the 1973 ruling.
But abortion is only one of many issues in which the court's moderate-to-liberal bloc of four justices has joined with the moderately conservative Justice Anthony Kennedy to form a precarious majority - one that would probably be undone by a McCain appointee.