America is very evenly divided. A 2% change in voting patterns can often change an election. There are many hardcore committed Ds and Rs, but there is also a mush middle.
What happened in the last eletion is the press when 100% negative on the R's and moved the mushiest part of the mushy middle to the D column. That 2% - who don't know what they think or have a political philosophy - do watch Good Morning America or listen to CNN at night.
To win most elections you need to deliver your base AND get a big percent of that mushy middle to go for you. Rove & the RNC won two elections with increasing the base but not really appealing to the middle. We got lucky with horrible candidates in Gore and Kerry, and a surge in latent patriotism around 9/11 in 2004.
In 2006 the chickens came home to roost. If the GOP wants to win the DO need to secure their base (if they have one left after this) but they also need to forcefully message to the Good Morning America crowd, some simple easy to digest message. Last time the D's used "culture of corruption" and won.
Sadly, it really is that simple.