Partisans also are fighting over the judicial balance of power in individual appeals circuits, Gerhardt said. One reason appointments to the D.C. Circuit are so contentious is that Republicans now have an edge of just a single vote on the court, with four justices appointed by Republican presidents and three appointed by Clinton.
There's also an element of payback at work, Wheeler said.
"Republicans don't think Bush's nominees were treated fairly," Wheeler said. "The Democrats would say that Bush was nominating a fair number of fairly radical people."
The expanding field of combat is damaging the federal judiciary by discouraging candidates, particularly attorneys who give up taking on new clients during the confirmation process with no certainty of the outcome, Wheeler said.
"If you're among the best and brightest in the legal profession, why should you subject yourself to a long and drawn- out process of this sort?" he said. "If you're in private practice, you have a lot to lose."
Leonard Leo, executive vice president of the Federalist Society, a self-described conservative legal group, said the potential for elevation to the Supreme Court is "probably one element" in Republican senators' opposition to some appeals court nominees. Still, "no U.S. senator has ever said to me point-blank, 'I am going to oppose this nominee because he might be on the Supreme Court,' " said Leo, who was an outside adviser to Bush on judicial nominations.
Leo said as far back as Ronald Reagan's presidency Democrats gave heightened scrutiny at confirmation hearings to appeals court nominees who were likely Supreme Court candidates.
"Going after Supreme Court prospects is nothing new," he said. "The weaponry that's brought on the field is what's changed, and that's the filibuster, and that goes back to what the Democrats deployed with Estrada and others."