WASHINGTON - As speculation on who will succeed retiring U.S. Supreme Court Justice David Souter reaches fever pitch in Washington, some conservatives are eyeing Minnesota's still-vacant U.S. Senate seat as the cushion between whether a new justice will be a moderate liberal or one from the "hard left."

"It's pretty huge," said Kelly Shackelford, chief counsel for the Liberty Legal Institute, a conservative legal group in Texas. "The only thing that could stop Obama from choosing a hard-left radical judicial activist is the Republicans having the ability to filibuster."

That ability may depend on Minnesota's Senate seat, which would provide a 60th vote for the Democrats -- a filibuster-proof super majority -- if DFLer Al Franken prevails over Republican Norm Coleman's appeal to the Minnesota Supreme Court. Coleman is challenging an election-trial ruling last month that Franken won by 312 votes.

Others say a Franken victory would merely give the White House a little more breathing room in the Senate's Supreme Court confirmation battle.

"Maybe around the edges, it will create some comfort level to have the 60th vote there," said Marge Baker, executive vice president of the left-leaning People for the American Way. Baker said she expects Obama's choice to line up closely with her group on "core constitutional values of justice, equality and opportunity for all."

"He would do that whether he had 58, 59 or 60 senators," she added. "But having 60 senators will certainly make it easier to get that nominee through."

Close counts

While Supreme Court confirmation battles have become ritualized Washington trials-by-fire, Senate Republicans have been greatly diminished by the last two national elections and the recent defection of Pennsylvania Sen. Arlen Specter, who was the ranking Republican on the Senate Judiciary Committee, where the skirmishing begins.

One close recount observer, University of Minnesota political scientist Larry Jacobs, says that with the balance of Senate power now at a critical tipping point, every Senate vote matters. "Picking a Supreme Court justice is a little like shuffleboard or horseshoes, where being close is sometimes the key thing," he said. "The issue here, with 59, is that the last vote can really make a difference in terms of the shading of the kind of candidate or nominee who is going to be put forward."

Conservatives, mobilizing for the coming Supreme Court showdown over issues like abortion and gun control, see Franken as the safest of votes for the kind of Obama nominee they surely won't like. "There's no shortage of ardent liberal judicial activists, and I'm sure [Franken] will be an eager vote for liberal judicial activism," said Ed Whelan, president of the conservative Ethics and Public Policy Center.

Still, Jacobs and others say that having 60 votes in the Senate does not necessarily give Obama a lock on any candidate he wants. The White House also has to take into account Democratic centrists and conservatives like Nebraska Sen. Ben Nelson.

'Independent thinkers'

"You're going to see a lot of independent thinkers who look at these nominees," said Minnesota Democrat Amy Klobuchar, a member of the Senate Judiciary Committee.

Nor is it always easy to predict a nominee's voting record on the court. Philippa Strum, a senior scholar at the non-partisan Woodrow Wilson Center in Washington, said that almost 50 percent of Supreme Court justices have had voting records "that could not have been predicted when they were appointed."

Among them: Justice Souter, a Republican nominee opposed by feminists because of his record on domestic violence legislation who has become a reliable member of the court's liberal wing.

The Minnesota recount could add to the uncertainty of picking Souter's replacement in another way. If Franken prevails, the Democrats' expected effort to seat him pending a potential federal appeal by Coleman could play out just as the Supreme Court confirmation battle begins.

Said Jacobs: "There's a perfect storm shaping up that creates a historic conflagration."

Kevin Diaz • 202-408-2753