As much as I hate to say it, I don't think the Democrats are growing so much because of our message/radical left-wing San Francisco values of killing babies and hugging trees, but we are a more inclusive (and diverse) party than the Republicans. Our coalition is broader and stronger and growing more so than the Republicans'. The GOP should and must allow moderates and, dare I say it, liberals, back into the party or else they will downsize from a national/major party to a regional party that dominates only in the rural white and Bible Belt regions of the South and Great Plains. I don't know but I wouldn't like to be known as a "regional party." Brings back a time period, oh, say around 1860 in American history.
By inclusive, you mean like how Sestak isn't challenging Specter?
I think that the Democrats are growing so much partly because politics is cyclical and partly because Republicans so tacked themselves to Bush that when he tanked, the entire party went with him. No one wants to be associated with losers.