Numbers are available by state. However since 2004, Democrats gained about 700,000 voters and Republicans lost almost 1 million.
This article presents the historical development and role of political parties in United States politics, and outlines more extensively the significant modern political parties. Throughout most of its history, American politics have been dominated by a two-party system. However, the United States Constitution has always been silent on the issue of political parties; at the time it was signed in 1787, there were no parties in the nation. Indeed, no nation in the world had voter-based political parties. The need to win popular support in a republic led to the American invention of political parties in the 1790s. Americans were especially innovative in devising new campaign techniques that linked public opinion with public policy through the party.
The United States is a federal constitutional republic, in which the President of the United States (the head of state and head of government), Congress, and judiciary share powers reserved to the national government, and the federal government shares sovereignty with the state governments. Republican Party
The United States is a federation, with elected officials at the federal (national), state and local levels. On a national level, the head of state, the President, is elected indirectly by the people, through an Electoral College. Today, the electors virtually always vote with the popular vote of their state. All members of the federal legislature, the Congress, are directly elected. There are many elected offices at state level, each state having at least an elective governor and legislature. There are also elected offices at the local level, in counties and cities. It is estimated that across the whole country, over one million offices are filled in every electoral cycle.
State law regulates most aspects of the election, including primaries, the eligibility of voters (beyond the basic constitutional definition), the running of each state's electoral college, and the running of state and local elections. The United States Constitution defines (to a basic extent) how federal elections are held, in Article One and Article Two and various amendments. The federal government has also been involved in attempts to increase voter turnout, by measures such as the National Voter Registration Act of 1993.
The Pennsylvania Democratic Party is the affiliate of the Democratic Party in the state of Pennsylvania. The party has had strong support in the Pittsburgh and Philadelphia area for a long time, having controlled the mayoral office in Philadelphia since 1952, and the Pittsburgh Mayoral office since 1933.