BURLINGTON, Vt.

Everyone expects this year's presidential election to be decided by razor-thin margins in a few battleground states. Everyone also expects the candidacy of Ralph Nader to make the race between John Kerry and George Bush even closer. As I know from experience, however, voters have a way of proving everyone wrong.

Democrats are motivated to defeat the president this year. They've seen firsthand what three years of Bush administration policies have done to America. And they want to stop his policies from inflicting any more damage on working-class Americans, the environment, our international standing or a woman's right to choose.

Many Democrats also admire Ralph Nader's achievements, as I do. But if they truly want George Bush out of the White House, they won't vote for Ralph Nader in November.

Ralph Nader has built a remarkable legacy as a consumer advocate. Because of his tireless work, we have federal consumer protection laws and a federal department dedicated to the protection of our environment, and millions of defective motor vehicles are off the roads. And I campaigned against the very same corporate special interests that he has been criticizing longer than almost anyone else.

But I don't believe that the best way to do justice to Ralph Nader's legacy is to vote for him for president. Re-electing George Bush would undo everything Ralph Nader has worked for through his entire career and, in fact, could lead to the dismantling of many of his accomplishments.

Voting for Ralph Nader, or for any third-party candidate for president, means a vote for a candidate who has no realistic shot of winning the White House. To underscore the danger of voting for any third-party candidate in elections this close, a statistic from the 2000 campaign may prove useful: a total of eight third-party candidates won more votes than the difference between Al Gore and George Bush nationwide.

When I ended my bid for the presidency, I asked my supporters to continue our quest for change in America. Our group, Democracy for America, is committed to exposing the ways in which the Bush administration's policies are designed to prop up the privileged and please right-wing ideologues. Our agenda is rooted in hope and real American values — opportunity, integrity, honesty. This is the way to defeat George Bush.

Ralph Nader once said that your best teacher is your last mistake. Too many of us learned the consequences of not standing together four years ago. This November, we can elect a president who fights for average Americans. But we can achieve this goal only if we join together — and don't repeat our last mistake.

Howard Dean, the former governor of Vermont, ended his candidacy for the Democratic nomination for president in February.