Political parties are non-governmental political purpose organizations (NGPPO's). The only true members of political parties are the elected government officials themselves, party organization officials, and all candidates from the party while running in elections for public office. American voters are not actual members of their party. Voters are customers.
Political parties are an association of individuals whose primary purpose are to promote or accomplish elections or appointments to public offices, positions, or jobs. A committee, association, or organization which accepts contributions or makes expenditures for the purpose of influencing or attempts to influence the election of presidential or vice presidential electors or of any individual whose is presented for election to any federal, state, or local elective public office (Blacks 6th Ed., p. 1158).
In political science acadamia, it is generally agreed that the political party era in the United States officially began in 1829 with the election of Andrew Jackson. It can be easily argued that it has been a Trail of Tears ever since. Political Parties in the United States do not derive their legitimacy from Article 4, Section 4, "Republican Form Guarantee Clause," or from any of the seven Articles which comprise the United States Constitution. Political Parties derive their right to exist through the Bill of Rights freedom of speech and right to assemble (see Madison No.10). However, when political factions seek to thwart civil society, those parties can be held accountable if and when they lose political power.
The organization and incorporation of political parties is based upon custom and usage law, which in turn has formed into a form of squatters rights.