Flip-Flopping: How much does it affect one's candidacy?

[Lemur]

Barack Obama, while running for the US Senate in 2004, said he believed in the decriminalization of marijuana. Now, while running for President, he declares that it is not a good idea.

Ummm ...

When asked by The Times about decriminalizing marijuana, the Obama campaign reiterated the candidate's opposition to legalization. "Senator Obama does not believe in legalization of marijuana, but agrees with President Bush that long minimum sentences for first-time drug users may not be the best way to occupy jail space or heal people from their disease," Obama spokesman Tommy Vietor said.

The campaign went on to say that, as president, Mr. Obama "will review drug sentences to see where we can be smarter on crime and reduce the blind and counterproductive sentencing of non-violent offenders, and revisit instances where drug rehabilitation may be more appropriate." His campaign later stated that Mr. Obama "always" has supported decriminalizing marijuana.

Given what Obama seems to mean by decriminalization, this position is not exactly radical. About a dozen states are said to have decriminalized marijuana, which generally means that possession of small amounts for personal use does not result in arrest and can be punished by a modest fine at worst.

-edit-

As for the opening question, I think it's useful to break it into two parts: What is the cause and cost of real flip-flopping, and how important is it to portray your opponent as a flip-flopper, whether it's true or not?