So when did this standard of maintaining the Supreme Court's balance start?

Today in OpinionJournal's Political Diary, John Fund writes:

. . . . But in 1993, when President Bill Clinton nominated former ACLU attorney Ruth Bader Ginsburg to fill the seat of retiring Justice Byron White, a conservative, there was no such wringing of hands about an impending ideological shift on the court.

An analysis by David Boaz of the Cato Institute found that major newspapers used the phrase "shift the court" 36 times in covering the Alito nomination. They referred to changes in the "balance" of the court another 31 times and used the phrase "shift to the right" 18 times.

By way of contrast, not a single major newspaper used any of those phrases when the Senate considered the Ginsburg nomination, though her appointment would clearly change the ideological makeup of the Court. Ms. Ginsburg was a noted liberal, while Justice White had voted in the minority in such key liberal decisions as Roe v. Wade and the Miranda ruling. He also wrote the majority opinion in Bowers v. Hardwick, the 1986 case that upheld the constitutionality of laws against homosexuality in some states. That decision was later overturned in the Lawrence case by a Supreme Court that included Justice Ginsburg. Indeed, the libertarian Institute for Justice has concluded that Justice Ginsburg is the most consistently liberal justice sitting on the Supreme Court today. . . .