Painting takes place in the realm of popular culture. It is relatively easy to be painted if you are relatively unknown on the national stage as all of the Democratic candidates are.
To counteract painting, the candidates must actively engage the media machine that enables painting. The simplest way is to appear as frequently as possible on popular TV shows such as Leno, Letterman and Oprah and to appear as warm as possible. Especially effective is to use self-deprecating humor. Reagan was a master of this.
It's best that this is done before serious damage from painting is done, but it will likely work afterwards as well.
Two current examples:
Dean-- after the Iowa caucus speech he is need of some positive image reinforcement. Given how widely played his speech is, he probably could easily get on evey popular talk show in the next few days and poke a little fun at himself. It would benefit him immensely.
Clark-- is being setup as an untrustworthy fellow.
He should be inoculating himself against these attacks by appearing on these shows and cracking a few jokes.
Btw, a corollary of this is that once you have a popular cultural stereotype it is hard to lose, both positive and negative. Jerry Brown's national political career was washed up as soon as he earned the moniker "Governor Moonbeam" to type his flakiness. Bush is sitting pretty because outside of people with strong partisan liberal preferences Bush has been stereotyped as a "man of integrity," if perhaps not the brightest guy. This all works to his advantage, because it is difficult to paint him against type. Barring "traitorgate" or another scandal dominating headlines in the coming year, direct attacks on his integrity will not likely work. They will be brushed off as partisanship by the apolitical. He first must be attacked more subtley, like making reference to how impressive it is that he has turned around a life of profligacy so late in life, etc. After the idea that he might not be all he seemed begins to circulate, it will be possible to attack him diectly.
I am providing a poll to see who everyone thinks is the most teflon-coated Democratic candidate.