Great Quote from 1927

Here in the last generation, a development has taken place which finds an analogy nowhere else.  American parties have ceased to be voluntary associations like trade unions or the good government clubs or the churches.  They have lost the right freely to determine how candidates shall be nominated and platforms framed, even who shall belong to the party and who shall lead it.  The state legislatures have regulated their structure and functions in great detail."

Source: American Parties and Elections,
 by Edward Sait, 1927 (Page 174)
 Quoted from: The tyranny of the two-party system,
 by Lisa Jane Disch c2002

In the past a political party was a private organization with a constitution.  It's members or their elected representatives could write a party platform. Any political candidates would be required to agree to the platform if they wished to run under the party's ballot name.

To the best of my knowledge, in most other democratic nations this is still the case! For one thing, many other nations have signed the Copenhagen Document of the Helsinki Accords into national law.  The Copenhagen Document of the Helsinki Accords states in part:

(5.4) - a clear separation between the State and political parties; in
particular, political parties will not be merged with the State;

(7.6) - respect the right of individuals and groups to establish, in full freedom, their own political parties or other political organizations and provide such political parties and organizations with the necessary legal guarantees to enable them to compete with each other on a basis of equal treatment before the law and by the authorities;...

Some of you are probably aware that, most U.S. states require nomination by primary election.  This started in the big cities in the 1880's.  One of the reasons this was done originally was to limit the ability of immigrants and the urban poor from using the right of association effectively in politics. At the time the stated desire was to "Break the Political Machine!” or "Destroy the Political Bosses!"  Of course another name for this "machine" is a private political organization, and "political bosses" included elected leaders of those private member based political organizations.  Later this was slowly extended to state, and congressional elections, to limit the ability of the middle and upper-middle class to organize effectively at those levels

By requiring, as opposed to allowing political parties to nominate candidates by public primaries, the state eliminates the effective power of party organizations.   Political parties technically still exist, but now they have no control over the candidates that run under the parties name!
 
A voter in a primary election is voting for a single candidate not a political party.  The fact that they have chosen to run under a specific political label means very little. It's important to remember that one elected politician cannot pass a law!  One elected politician cannot even get a bill out of the committee!

A modern "party" candidate is just an individual that competes in a single election district. By registering with the state as a member of the party label of their choice - just like any voter who wishes to vote in primary elections (excluding hefty fees & many reporting requirements) - they may choose to run under labels such as Republican, or Democrat, or any other party that has achieved similar ballot status!  I would not view them as members of any political party, in either the traditional or international sense. There is no citizens organization, or party leader, that has the power and responsibility for these labeled politicians.

In the absense of the traditional dues paying, member based, association of citizens that organize politicians under a party ballot label, politicians are organized by other means.  The following two articles from this website provide further information.

Modern Party Platforms

Our National Committees: Ever wonder what they do?

?GOP?

? ?

Chesire Cat Politics

Modern U.S. attempts at realistic political party platforms.

One elected politician cannot pass a law. One elected politician cannot even get a bill out of the  committee! Obviously the voters would tend to be very interested in political platforms.

Politicians could organize themselves, or be organized by money, or be organized along party lines by the party leadership or any combination of those.