Representing Middle class interest
Jared Bernstein has a couple of Graphs that are worth a thousand words. The first graph displays the evolution of real median familly income over the past two decades. The second plots real median income growth in two periods: from 1992 to 2000 and between 2002 and 2007.
What this shows is that rule by the democratic party has been much more successful at advancing workers' wages. So, it does make a difference who is in power and the Republicans have been either unwilling or unable to promote real income growth.