In all functioning democracies, there is a minority who are wealthy and a majority who are not. Human nature being what it is, the wealthy minority does not want a government which will take its wealth and give it to the non-wealthy. They therefore form a political party to protect their interests. This is known as a conservative party. It goes by different names. In Australia it is called, oddly enough, the "Liberal Party". To represent the interests of the non-wealthy, specifically non-management employees, there is a large socialist party. Even in a multi-party system, these two party types dominate a nation's politics.
In America, our conservative party is the Republican Party. We are unique in that we don't have a major socialist party. The Republicans' opponent is the Democratic Party which is a capitalist party that is a combination of left-wing, centrist and right leaning elements. If economics were the only political issue, the conservatives would never win any elections. However most voters are concerned about many issues. Especially in America, where for many voters social values and other non-economic issues are as important or more important than economic issues. Since the base of each party is a minority, it is necessary to appeal to centrist voters to win elections. The normal result is one main party is center-right and the other is center-left.
Until 1980 the Republican party was a normal center-right party. With the election of Ronald Reagan it began moving steadily to the right. Today it is a far-right party that is not connected with reality. This has produced an internal crisis in the party at the national level. There is a split between the establishment Republicans who are practical politicians and the Tea Party fanatics. There is also growing tension with the religious right base which is losing patience with the party establishment.
The Democratic Party has also moved to the right, starting with Jimmy Carter who was socially and politically liberal but economically conservative. He believed that the free market was better than a regulated market. He deregulated the trucking and airline industries. Bill Clinton continued the process by pushing through NAFTA (the North American Free Trade Act), deregulating the banking industry (he repealed the Glass-Steagall Act of 1932) and preventing the regulation of exotic new types of derivative financial instruments. Many financial experts warned that they were dangerous. Billionaire investor Warren Buffet called them "financial weapons of mass destruction." The repeal of Glass-Steagall and massive sales worldwide of the new type derivatives were the main reason for the global financial collapse in 2008- not the widespread granting of high-risk subprime mortgages as most people believe. (In spite of the devastation of the Great Recession/Global Financial Crisis, derivatives are still not regulated. No one even knows how many trillions of dollars in uncollateralized derivatives are floating around in the global financial system.)
The modern Democratic party is not the party of Franklin D. Roosevelt and the New Deal when it comes to economics.