In Judo you use the opponents one weight against them. We are at a supposed disadvantage, we have no clear candidate. However we can use this to our advantage, the Republicans have no clear target while we have our target, McCain.
We need to pin him to Bush. That infamous hugging photo needs to go memetic in the mainstream. We could, for example, create funny YouTube montages of the photo and work on making it go viral. We also need to bring up the age issue, while it may seem unfair 72 years old does seem like an inappropiate age at which seek the presidency to me.
We also need to hammer home our message on Iraq, economics, healthcare and ( crucially) the enviroment(1). We need to do so against an anti McCain background. McCain admitted to not knowing very much about the economy and the media gave him a free pass!
We also need to target Huckabee, who looks almost certain to get the VP nod. We need to bring to light the whacky things he's said about changing the constitution, and we need to get it outside of the leftie blogsphere into the mainstream internet and even media.
Perhaps not having a clear candidate is not a disadvantage afterall. It really depends on how well we utilise the chances McCain gives us.
(1)- The enviroment is an underexploited issue in American politics, even if it cannot turn the tide of this election focusing on the enviroment, and our better policies on it, helps put us in a strong position.