"I'm increasingly concerned about the current climate of challenge to judicial independence," O'Connor told a gathering of state judges from around the country Friday. "Unhappiness with judges today is at a very intense level."
The judiciary is the weakest of the three branches of government, she said, and therefore the one with "the greatest need to be defended."
The executive and legislative branches have become the attackers, so "the principal defenders are going to have to be the people of this country," with lawyers taking the lead, she said.
O'Connor, who retired in January after 24 years on the nation's highest court, spoke just days before South Dakota voters consider the "Jail 4 Judges" initiative. It would create a citizens' grand jury that could authorize lawsuits or criminal prosecutions against judges based on their rulings.
Colorado voters will decide whether to limit judges on the state's highest courts to 10 years in office, a measure that would remove five of the state's seven Supreme Court justices within two years.