Liberals want President Obama to find a progressive nominee for the Supreme Court who is "an intellectual giant, and also passionate, persuasive, and politically savvy enough to build consensus and outfox the court's conservatives" -- someone not unlike Justice William J. Brennan Jr., who retired from the court in 1990. But the modern day Supreme Court may not be a hospitable place for a consensus builder in Brennan's mold, writes Seth Stern.