WITH JOHN ROBERTS sailing toward confirmation last week, President Bush had the O'Connor seat "won." The Court was set to move one click to the right (so to speak). Then Chief Justice William Rehnquist died. The president chose to move Roberts over to fill the Rehnquist slot--thereby re-opening the vacancy created by Sandra Day O'Connor's retirement.One understands the attraction of Roberts as chief. But with this action, in one fell swoop, the president deprived himself and his supporters of the easiest argument for his next nominee: that surely a reelected conservative president is entitled to replace a conservative justice--Rehnquist--with another...