The nature of each party’s coalition explains each party’s lawmakers’ positions on policy issues, through lawmakers’ need for voter support (party alignment) and financial donations. Therefore, they are likely to vote on policy issues in such a way that benefits from that policy are concentrated among their constituents and benefactors and costs are dispersed among a broad base.
Historically, party alignment has depended on and changed with significant historical events such as the Civil War, the Great Depression and the Civil Rights movement. Most recently, party alignment has been determined by disagreement over social issues. As these issues also reinforce each other, this has led to party polarisation. During campaigns many voters are already aligned with one of the two parties. The Democratic party coalition is made up of diverse socially progressive groups and minorities. Individual voters are allied with the party through these groups and the Democratic platform can therefore be described as an “aggregation” of these groups interests (Grossmann and Hopkins, 2016). In contrast, the Republican party coalition is united not through interest groups, but through their conservative ideology of “limited government, American nationalism and cultural traditionalism” (Grossmann and Hopkins, 2016).
Religion has been an important factor in American politics. Today, secularists and liberal religious groups tend to vote for the Democratic party, and religious conservatives tend to vote Republican. This is a result of the emergence of social issues such as abortion and gay rights. Both issues can be rejected based on religious doctrine and conservative values, e.g. traditional family values. Thus, Republicans tend to be pro-life and for limited or no expansion of gay rights. Democrats, backed by interest groups, tend to be pro-choice and in favour of gay rights – Planned Parenthood contributed a total of $694,179 to congressional campaigns in the 2016 cycle, and though officially non-partisan, 98% went to Democratic candidates (Kiely, 2017). Similarly, there is a split in policy decisions when it comes to fiscal and monetary issues. Republicans tend to support supply-side economics (e.g. 2001 Bush tax cuts), because it directly supports financiers and voters in their base. This type of policy provides economic benefits to the wealthy and to corporations, with the idea that their economic activity will in turn benefit lower income groups. Democrats, on the other hand have a preference for demand-side economic policy, because their coalition tilts towards lower incomes; stimulus bills (e.g. 2009 Obama stimulus bill) put money directly in the hands of the consumer. Another example can be found in regulatory issues. Here, Republicans ideologically support limited government and thus they tend to oppose increased regulation and government intervention. This also greatly benefits their corporate donor and supporters. Democrats, on the other hand are supported by e.g. environmental interest groups and therefore Democratic lawmakers are more likely to support regulation.
Thus, lawmakers are inclined to take positions that sit well with their constituents and donors, and in the American two-party system that means polarising issues often put the parties up against one another. For social issues this means Democrats are more likely to take a liberal position, and Republicans a conservative position; for fiscal and monetary issues this means Democrats are more likely to favour supply side policy that benefits lower income groups, and Republicans are more likely to favour demand-side policy that benefits higher income groups; for regulatory issues this means Democrats are more likely than Republicans to support government intervention.
Grossmann, M., Hopkins D.A. (2016, September 8th). How different are the Democratic and Republican parties? Too different to compare. Available online at: https://www.washingtonpost.com/news/monkey-cage/wp/2016/09/08/how-different-are-the-democratic-and-republican-parties-too-different-to-compare/
Kiely, E. (2017, February 2nd). Planned Parenthood and the Democrats. http://www.factcheck.org/2017/02/planned-parenthood-and-the-democrats/