A survey released Wednesday by Public Policy Polling found President Obama leading Sarah Palin by 20 points in a hypothetical 2012 presidential race. Three and a half years before the actual election will take place, the poll served as a reminder of exactly how much things can change in a relatively short amount of time.

It's sometimes hard to remember what conventional wisdom was four years ago, shortly after George W. Bush began his second term in office. Most might remember that, as evidenced by an August 2005 Gallup survey, New York Sen. Hillary Rodham Clinton was the odds-on favorite to win the Democratic nomination. This was just a year after anyone outside of his Illinois State Senate district had ever heard of Barack Obama, whom Gallup didn't even include in the poll.

At that time, however, most Washington insiders felt Clinton had little chance of winning the general election -- as this July 2005 Washington Monthly piece illustrates. She was seen as too liberal, unable to win swing voters and vulnerable to inevitable Republican attack ads. Less than three years later, many saw Clinton as just the opposite, and her supporters were using those same arguments during the Democratic primaries for why Obama could not win.

Democratic insiders today may not fear a potential challenge from Palin, who -- like Clinton four years ago -- could be seen as too polarizing to pick up enough independent voters. While Palin certainly didn't appear ready for a presidential bid last year, who's to say she won't be three years from now? Palin was mayor of a town with less than 10,000 people just three years ago. Now she's being polled against the President of the United States.

In politics, three years is a lifetime.