The news of 89-year-old Justice John Paul Stevens' likely retirement from the Supreme Court caused little excitement and with good reason. Liberals and conservatives alike assume President Obama will appoint another reliably liberal justice and the Senate will promptly confirm the choice.

That's the way it has gone with the nominees of Democratic presidents going back decades. That, however, is not the way it has gone with Republican presidents and their nominees. If it had, the court and therefore the country would be much more conservative than it is.

But Richard Nixon nominee Harry Blackmun ended up writing the opinion that found a right to abortion that had previously gone undetected in the Constitution.

Nixon successor Gerald Ford nominated Stevens, who has ended up the leader of the court's liberal wing.

Ronald Reagan nominee Sandra Day O'Connor moved the court slightly right, but only slightly. And Reagan's nomination of the brilliant and staunchly conservative Robert Bork was defeated by the Senate on purely ideological grounds which led to the appointment of Justice Anthony Kennedy. He has ended up not as a reliable conservative but the court's swing vote.

People are generally thought to become more conservative as they grow older. That has often not been true of Supreme Court justices. So far, George W. Bush nominees John Roberts and Samuel Alito have remained conservative. But they're still young men by Supreme Court standards.

Brit Hume is the senior political analyst for Fox News Channel.