For the most part, U.S. Supreme Courts have followed the legal principle of stare decisis – “let the decision stand.” In other words, the court has already set the precedent, and later decisions should follow it.

There have been exceptions, of course, but they are so rare that they prove the rule. Probably the best known is the 1954 decision in Brown v. Board of Education, which overturned the court’s 1886 ruling in Plessy v. Ferguson. That earlier ruling allowed “separate but equal” schools, a decision that permitted government-sponsored segregation.

Even though a majority of the nine justices today are conservative and even though many people would like to see the court overturn the 1973 Roe v. Wade ruling, so far it hasn’t.

While it’s possible for a court to overturn a precedent, the chances that the very same justices will overturn a ruling less than three months old are zero.

That, in essence, is why Indiana Attorney General Greg Zoeller said he would not try to defend portions of Indiana’s anti-immigration law that were similar to the Arizona law. Like it or not, the Supreme Court has ruled parts of the Arizona law are unconstitutional, and the justices aren’t going to change their minds, at least any time soon.

Yes, Zoeller could seek to uphold the Indiana law in federal court – and then in the federal court of appeals, and then in the Supreme Court, but the rulings would ultimately say, to put it simply, “already decided.” The decision has been made, and trying to appeal it now would be a waste of state government’s (taxpayers’) time and resources.

But that hasn’t stopped anti-immigration state Sens. Mike Delph of Carmel, Brent Steele of Bedford and Phil Boots of Crawfordsville from criticizing Zoeller’s decision. They are seeking to defend the Indiana law against a court challenge. Like Zoeller, the three senators are all Republicans.

Some progressives would argue Zoeller has been too conservative as attorney general, defending Treasurer Richard Mourdock’s appeals to stop the Chrysler reorganization and joining other states to fight the federal health care law. And Zoeller has displayed initiative where other attorneys general may have waited: he was out front in deciding how the state should compensate victims of the Indiana State Fair stage collapse and in dropping a state agency’s efforts to restrain an Indiana newspaper from publishing a story.

As a spokesman pointed out, Zoeller aggressively defended the Indiana immigration law until the U.S. Supreme Court ruled states could not do what Arizona – and Indiana – was attempting. That Supreme Court ruling is now the law, and Zoeller is obligated to follow it.