I have wondered about this for some time, particularly because there are plenty of Democrats who are not progressive, which I have found hard to comprehend. There has to be something more fundamental that distinguishes Democrats from Republicans, even when they seem to be kind of right-wing Dems.
Imagine a fundamental societal unit: a family. It can be a nuclear family or an extended family, it doesn't matter. Each member of the family supports the others in some way. When one member does well outside the family, it is largely due in some manner to support provided by the family.
This is where the difference between Democrats and Republicans comes in. Democrats recognize that the support from the family was instrumental in the individual's ability to develop separate assets. This obligates the individual to provide some of those assets back to the family, while potentially extracting fewer resources from the family due to reduced personal need.
Republicans see this completely differently. The individual, entirely through personal ingenuity and hard work, has gained assets from outside the family. Those are his or her own property and he or she does not need to share it. Additionally, the individual may still expect a share of the family resources.
Although no one is saying that all of the assets earned by the individual have to be shared with the collective, Republicans would have us all believe that it is the true Democratic agenda. They contend that the Democrats want to "spread the wealth around." And unfortunately, too many people out there have bought into this, and this is why our infrastructure is crumbling, and people who want to work are unemployed, and we are so incredibly divided between the haves and have-nots.
Just my $.02 that I'm contributing to the collective.