Another strategy for wishing away the court's ideological fractures is to tout the ability of a consensus-building Justice to wield enormous influence on the court. This notion, often accompanied by the suggestion to add a politician to the current court (which has none), has little application to the modern court.
Historically, a rare few Justices have been able to use their extraordinary political skills to build bridges and meaningfully influence the court's direction. The most notable example is Earl Warren, who was able to convince fractious colleagues to unite behind his unanimous opinion in Brown v. Board of Education overturning the doctrine of separate but equal and declaring segregated public schools unconstitutional. William Brennan, Warren's top lieutenant, also used his canny diplomatic skills to help guide the court through some very difficult moments, as when he forged unanimity behind the decision forcing President Richard Nixon to turn over the White House tape recordings that would ultimately lead to Nixon's resignation.
But the impact of interpersonal or political skills is overstated. Chief Justice John Roberts entered with high expectations that his much-admired interpersonal skills would create greater collegiality at the court. He even set this as a goal. But the ideological differences on the high bench are too big to be bridged by personality. The Roberts Court has split predictably 5-4 on almost all the hot-button issues. And Roberts himself has become more hard-edged and divisive, as his views on issues of race and executive power have clashed repeatedly with those of the court's liberal wing.
On today's court, the most powerful Justice is Anthony Kennedy. His power comes not from the art of persuasion (which Kennedy rarely practices) but from the simple arithmetic that five votes beats four and Kennedy's is the swing vote on almost every issue. Meanwhile, the most influential Justice is the court's least diplomatic Antonin Scalia. Although he writes opinions that are bombastic and even insulting to other Justices, and although he's never been able to forge a working majority for some of his most important initiatives (like overturning Roe v. Wade), through sheer force of intellect and a bullying style, he has succeeded in profoundly changing the court's entire methodology for interpreting statutes and has made respectable a mode of conservative constitutional interpretation "originalism" that would likely be moribund without him.