Souter was firmly among the court's liberals. . .Notice that "liberal" = "middle ground"?
Of the justices who occupied the high court's middle ground, Souter was the one most likely to challenge, in exchanges of written opinions, the aggressively conservative views of Justice Antonin Scalia.
BTW, even the New York Times rates Souter the third most liberal current Justice.
(via The Corner, TigerHawk)