The democratic party has, traditionally, been the more blue collar friendly party in America. Democrats tend to back social welfare programs that aid the poor. They also back unions that support and defend blue collar works and ensure that they receive fair pay and benefits. Republicans usually take a more trickle down approach to social and economic reform, which provides little benefit in the form of direct relief to lower-income Americans.
Republicans are all about benefiting big business with tax breaks for the rich. Democrats are more apt to give money directly to the poor. Giving more money to the rich doesn't guarantee more spending money for the poor or more jobs. Money for the poor means more spending in the consumer-based economy, which Democrats favor.