The war in Iraq is a mess, and the immigration bill appears dead. But one branch of government is working out as President Bush planned.

It’s the Supreme Court, which ended its 2006-07 term Thursday with rulings on a Texas death penalty case involving the mental health of a double murderer and two affirmative action cases.

Previous decisions this term indicate that, by installing Justices John Roberts and Samuel Alito, Bush already has come closer than either Ronald Reagan or his own father toward achieving the long-held conservative goal of a solid Supreme Court majority.

It could become one of his most lasting presidential legacies.

The impact of his two nominees was underscored this week by a trio of decisions. One limited the rights of citizens to sue over perceived violations of the separation of church and state. Another supported high school authorities who suspended a student over a banner they said challenged their anti-drug message.

In two of the cases, Roberts wrote the opinion for a 5-4 majority; in the third, Alito did. Earlier this year, their votes enabled the court to reverse its prior position and uphold the law banning a controversial late-term abortion procedure, one of several 5-4 rulings in which they helped to forge a conservative majority.

Thus, a strong pattern has emerged, although in some cases, the scope of rulings has been sufficiently narrow to limit their impact as precedents.

Nevertheless, the emergence of what court-watchers are already calling the Roberts Court has raised the stakes on the 2008 election. It may well determine the degree to which the chief justice will be able to maintain a conservative majority the next few years.

That’s because the three justices most likely to leave the court are all members of the liberal-to-moderate bloc that was outvoted with increasing frequency in the just-ending court term.

They are John Paul Stevens, 87, the court’s oldest and longest-serving justice; Ruth Bader Ginsburg, 74, whose health has been questionable; and David Souter, 67, who reportedly yearns to spend more time in his native New Hampshire.

Election of another Republican president who could replace just one of them with someone in the Roberts-Alito mold might cement the conservative majority.

Election of a Democrat who could replace any of them with a like-minded justice would bolster the court’s liberal-to-moderate bloc and enable it to expand into a majority if one of the conservatives left.

This assumes that the current nine members stay through next year’s election. There have been no recent rumors of retirements, and it’s widely believed that Bush would have difficulty winning confirmation of another conservative justice from the Democratic Senate.

It doesn’t mean he won’t try.

Several weeks ago, ABC’s Jan Crawford Greenburg, one of the most astute court-watchers and author of a recent book about the administration’s effort to push it to the right, wrote on the ABC News Web site that the White House is developing a short list of possible nominees in the event of a vacancy.

According to Greenburg, Bush told aides he wanted to nominate a woman or a minority, and his short list included several conservative women mentioned for prior openings, including Judges Priscilla Owen of Texas and Janice Rogers Brown, a black from California now sitting on the federal appeals bench in Washington.

The conventional wisdom is that the Democratic Senate would block such a nomination, bottling it up in the Judiciary Committee or preventing a floor vote.

But a prominent conservative commentator, Ed Whelan, recently rejected such thinking as “unsound,” noting at National Review Online that enough Democrats are politically vulnerable in conservative states that the Senate would have to give any nominee an up-or-down vote.

Given the way Democrats are playing “hard ball” with Bush’s choices for the appellate courts, that may be wishful thinking.

But Democrats probably hope the situation won’t arise, leaving any vacancies up to the next president at a time when they have good reason to believe it may well be a Democrat.