With President Bush and the Republican Party on the rocks, many Democrats think the 2008 election will be, to borrow a favorite GOP phrase, a cakewalk. Some liberals are so confident about Democratic prospects that they contend the centrism that vaulted Democrats to victory in the 1990s no longer matters.

The temptation to ignore the vital center is nothing new. Every four years, in the heat of the nominating process, liberals and conservatives alike dream of a world in which swing voters don't exist. Some on the left would love to pretend that groups such as the Democratic Leadership Council, the party's leading centrist voice, aren't needed anymore.

But for Democrats, taking the center for granted next year would be a greater mistake than ever before. George W. Bush is handing us Democrats our Hoover moment. Independents, swing voters and even some Republicans who haven't voted our way in more than a decade are willing to hear us out. With an ambitious common-sense agenda, the progressive center has a once-in-a-lifetime opportunity to win back the White House, expand its margins in Congress and build a political and governing majority that could last a generation.

A majority comes hard for Democrats. In the past 150 years, only three Democrats, one of whom was Franklin Roosevelt, have won the White House with a majority of the popular vote.

What's more, political success built on the other party's failure is fleeting. Jimmy Carter won a majority in the wake of Watergate, but his own shortcomings on national security and the economy took him from majority victor to landslide loser in four years. Repudiating the other side's approach is only half the battle. Since neither side has a monopoly on truth, the hard part is knowing when to look beyond traditional orthodoxies to do what works.

Like FDR, we can build a lasting majority only by earning it — with ideas that demonstrate to the American people that if they entrust us with national leadership, we can deal effectively with the challenges our country faces and the challenges they face in their everyday lives.

Over the past six years, we've seen what happens when an administration writes off the political center and manipulates every decision for partisan gain. Bush's failure to solve — or even address — America's great challenges has left our country dispirited, disillusioned and divided.

Contrast the collapse of a conservative president with the success of the last centrist president. Bill Clinton ran on an agenda of sensible ideas that brought America a decade of peace and prosperity. He was the only Democrat to be elected and re-elected president in the past seven decades, and he left office more popular than almost any other president in recent memory.

Nearly seven years after Bush succeeded Clinton in the White House, America is facing challenges as great as we've ever seen — a war against Islamist radicals who would destroy our way of life; global economic competition that demands we raise our game; and a quest for energy independence and efficiency that Al Gore has shown us could make or break our planet. To conquer such enduring problems, Democrats will need a broad, enduring majority — and a centrist agenda that sustains it by making steady progress.

Most Americans don't care much about partisan politics; they just want practical answers to the problems they face every day. So far, our leading presidential candidates seem to understand that the proof of the pudding is in the eating. That's why they have begun putting forward smart, New Democrat plans to cap and trade carbon emissions, give more Americans the chance to earn their way through college, achieve universal health care through shared responsibility, increase national security by rebuilding our embattled military and enable all Americans who work full time to lift themselves out of poverty.

As the caucuses and primaries approach, candidates will come under increasing pressure to ignore the broader electorate and appeal to the party faithful. But the opportunity to build a historic majority is too great — and too rare — to pass up.

A new Democratic president will have the chance to unite Americans around solutions that will make all Americans proud of their country again. For the sake of the hardworking Americans who are depending on us to fix Washington and put our country on the right track, we pray that Democrats set out to build a majority that can last.

Martin O'Malley, a Democrat, is governor of Maryland. Harold Ford Jr. is a former Democratic representative from Tennessee and chairman of the Democratic Leadership Council. They wrote this commentary for The Washington Post.