[George W. Bush]

If Dean is the nominee, Nader won't get anywhere.

If one of the other Dims is the nominee, Nader will run again and likely cost them key states like in 2000.

[zbigreddogz]

Even if Dean is the nominee, he could still steal a few thousand votes in a few key states.

However, if Dean is the nominee, I don't think it will matter. He'll win 10 states if he's lucky.