The most important reason to vote for Obama.

IN EVERY PRESIDENTIAL campaign since Roe v. Wade, the Democratic nominee has ominously intoned that the Supreme Court hangs in the balance. “We must win to save the Supreme Court of the United States,” Walter Mondale declared in 1984. “This election is about the Supreme Court,” Al Gore warned 24 hours before the polls closed in 2000. (As it turned out, he was right.)

This year, however, the future of the Court has barely received an obligatory nod from Barack Obama. It’s a surprising omission: Liberal alarmism about the fate of the Supreme Court has never more accurately reflected reality. Since the Reagan years, with a brief 6-3 interlude in the early ’90s, the Court has been divided between five conservative justices and four liberals, with no genuine opportunities for either side to meaningfully tilt that balance. A Mitt Romney victory, however, would likely obliterate the status quo, creating a solid 6-3 conservative majority. The shift would transform American law and politics to a degree that is difficult to overstate.

To put his stamp on the Court, Romney would need a vacancy—and in the course of four or eight years, he would almost certainly have at least one. Predicting a Supreme Court retirement, of course, is always difficult, but Justice Ruth Bader Ginsburg turns 80 in March. Last August, she told Reuters that she hopes to spend at least three more years on the bench, which would allow her to match the 23-year tenure of Justice Louis Brandeis. (“Brandeis had a problem I didn’t,” she said of her desire to continue. “He was losing his eyesight.”) Ginsburg, thankfully, seems fully recovered from surgery for pancreatic cancer in 2009, but her interview suggests that she may be ready to retire in the middle of the next president’s term, especially if Obama wins. If Romney beats Obama, she might well try to wait him out. But as Brandeis learned, delaying retirement is not always an option.

There’s no reason to doubt that a President Romney would replace Ginsburg with a conservative. He has loudly promised to appoint justices in the mode of Chief Justice John Roberts and Justice Samuel Alito, and all of the leading candidates on his presumed Supreme Court short list—including Paul Clement, the former U.S. solicitor general; Brett Kavanaugh, a judge on the U.S. Court of Appeals for the D.C. Circuit; and Diane Sykes, of the U.S. Court of Appeals for the Seventh Circuit—fit that mode: pro-business conservatives who are interested in expanding executive power at the expense of Congress.

The last time the Court shifted so dramatically was 1987. That Court was also divided 5-4, with a liberal-leaning majority. But the retirement of Justice Lewis Powell, a moderate, presented Ronald Reagan a chance to tilt the Court toward the right. His first ill-fated nominee, Robert Bork, would have prodded the Court in an even more conservative direction. The fact that Reagan was forced to settle for his third-choice nominee, Anthony Kennedy, has somewhat mitigated the new ideological course. But the stakes are even higher now. A sixth vote would end the long fascination with Justice Kennedy’s self-conscious agonizing, eliminating his ability to impose his idiosyncratic libertarianism on decisions; it would create an invincible conservative majority.