Washington ? Now we can have an election that is about 2004, not 2000.

Former Vice President Al Gore’s decision not to mount a third presidential campaign has dramatically altered the political landscape. It assures that the next election will be about the future, not the past. It means that the 2004 contest will be about the new issues of the new century, not about the old rivalries of the old dynasties. It means that the Democrats have a better chance of putting a new face forward in their effort to defeat President Bush.

The remarkable thing about American politics is how quickly it can be transformed — and how swiftly the noncombatants fade away. Gore and Rep. Richard A. Gephardt of Missouri were supposed to be the big Democratic hopes for 1992; they withdrew from the field in 1991, and the vacuum was filled by Gov. Bill Clinton of Arkansas, who dominated American civic life for nearly a decade. Now Gore is gone and the struggle to fill the new vacuum is on.

This is the second time Gore has done the hard but right thing. The first time came two years ago this month, when he conceded the election to Bush and told the country that “for the sake of our unity as a people,” it was time to move on and support a rival who had won fewer popular votes than he did. This time he told the country that Bush-Gore II would “inevitably involve a focus on the past that would in some measure distract from the focus on the future that I think all campaigns have to be about.”

Presidential rematches are seldom edifying; the last time we had one was in 1956, when Adlai E. Stevenson once again took on Dwight D. Eisenhower. It was a dreary affair; Stevenson had no issues and had to manufacture a rationale for his campaign. He came up with a proposal for a unilateral cessation of nuclear testing and emphasized President Eisenhower’s health, warning of the dark prospect that Vice President Richard M. Nixon could ascend to the presidency. Stevenson made little impact with either gambit, but his prospects were buried when international crises unfolded in late October 1956 in the Suez and Hungary.

Now it’s not as if Americans aren’t willing to relive old questions. In recent weeks, as the political crisis around Republican Sen. Trent Lott of Mississippi has deepened, the political world has been refighting the election of 1948, when Strom Thurmond mounted his states’ rights challenge to Harry Truman.

But had Gore remained in national politics, the next presidential race would have been about the following things: a debate about who lost Florida; a re-examination of Gore’s unwillingness to let Clinton campaign for him; a lengthy national seminar about justice; and a look at the fuzzy math of the past. Even Stevenson switched running mates between 1952 and 1956, replacing Sen. John Sparkman of Alabama with Sen. Estes Kefauver of Tennessee. Gore could not abandon Sen. Joseph Lieberman of Connecticut after Lieberman insisted he wouldn’t run if Gore did.

The rematch also would have also been about revenge, and even if Gore were to advance some new ideas or new policies, the revenge theme would never be far away. If you are looking for an analogue, try the current showdown with Iraq. The president has several reasons for wanting to disarm, or perhaps to fight, Saddam Hussein, but the notion of family revenge will never quite disappear.

It is remarkable how antiquarian the 2000 election looks from here, in the last weeks of 2002. It was fought in a time of peace and prosperity. A major issue was the dignity of the office of the presidency in the wake of the Clinton impeachment. Gov. Bush spoke often about the need to respect the military. Vice President Gore’s staff clucked about the fact that Bush couldn’t identify the prime minister of Pakistan. (No one doubts that now.)

The new issues of the new world are far different, and far more critical. The United States has been attacked by terrorists once, and now the phrase “homeland defense,” which would have had no meaning in the 2000 debates, is a top national priority. Two years ago the people who talked about military reform worried about what kind of tanks the Pentagon was buying. Now the Pentagon is talking seriously about mounting clandestine psychological and propaganda operations in the Islamic world.

During the Bush-Gore race, the nation was so prosperous (and the cult of the CEO was so strong) that nobody talked about corporate misconduct. Today, after the Enron scandal and the WorldCom debacle, the nation is a lot more wary — and much more worried.

All this is a reason why, as Gore put it in a rambling Raleigh, N.C., press conference Monday afternoon, the next election cannot be about what happened two years but about “where we are going from here.”

Those close to Gore say that the former vice president’s decision was difficult, particularly because he had dedicated his life to the pursuit of the presidency. He said in the North Carolina press conference that the conclusion came to him gradually, not as an epiphany. Some of his most intimate advisers were surprised by the decision. But of the many millions of people who did not relish a Bush-Gore rematch, only one could do anything about it. He was Al Gore, who in one gesture gave a new start to himself and to the country.

David Shribman is a columnist for The Boston Globe.