With the announcement that Ralph Nader is seeking the White House for the fifth time, Al Gore may have rolled over in his grave.

No, Al Gore isn’t actually deceased, but in the opinion of many Democrats, the death of his presidential hopes in 2000 came at the hands of one man - and that man is not named George W. Bush.

Siphoning more votes in several states than the margin by which Gore lost to Bush, Nader’s third-party candidacy may have swung the election to the Republicans eight years ago. Resentment lingers.

Nevertheless, Nader is once again entering the race as an independent, he announced Sunday, calling for a “Jeffersonian revolution.”

Ralph Nader, 73, explained the nature of his bid on NBC’s Meet the Press:

“Big money and the closing down of Washington against citizen groups prevent us from trying to improve our country. And I want everybody to have the right and opportunity to improve their country.”

Both Democratic contenders were quick to jump on Ralph Nader.

Calling Nader’s unsurprising entry into the race “very unfortunate,” Sen. Hillary Rodham Clinton said, “I remember when he ran before. It didn’t turn out very well for anybody - especially our country.”

“This time I hope it doesn’t hurt anyone. I can’t think of anybody that would vote for [John McCain] who would vote for Ralph Nader.”

Sen. Barack Obama offered similar criticism:

“He thought that there was no difference between Al Gore and George Bush and, eight years later, I think people realize that Ralph did not know what he was talking about,” he said.

While he praised Ralph Nader for doing “as much as just about anyone for American consumers” Obama said he is somebody who, “if you don’t listen and adopt all of his policies, thinks you’re not substantive.”

Nader called Barack Obama “a person of substance” but chastised him for “censoring his instincts” on some divisive issues.

What impact will this have on the race? Hopefully none. But a third-party bid invariably means potentially playing spoiler to someone.

Hypothetically (though with less of an impact), Ralph Nader’s bid is the equivalent of Ron Paul launching a libertarian run - which he won’t do.

For this reason, Democrats can’t help but feel queasy, even if both Clinton and Obama are strong candidates and backlash from Nader’s 2000 run will prompt fewer liberals to choose him again.

The past is the past, and Ralph Nader won’t gain much traction here in 2008. But when you consider what could have been - Al Gore being president for the past eight years - it’s hard not to dwell.