What functions have political parties served in American politics? Assess the strength of each aspect of the U.S. political parties—the party in government, the party as organizations, and party in the electorate.

The function of political parties is to present candidates for political office, have those candidates run in the parties name, and to win power when those candidates are elected.  Parties help candidates to solve the “social choice problem”, “collective action problem” and are a mechanism for elites to organize and communicate with voters.
Parties in government are strong.  Elected officials currently vote with the party on 90% of the issues.  The parties control the agenda, committee assignments, campaign contributions and fundraising, and encourage or discourage primary election challenges.  Parties are also strong with the electorate.  Only 13% of the population doesn’t associate with either Democrats or Republicans to some degree, and those who do associate with a party will generally vote for that party's candidates. Party organizations are also strong as they raise large sums of money (about $600-$700 million in the last presidential election for each party) and enlist volunteers for campaigns.  There is also a trend where party organizations are contacting and mobilizing voters at an increasing rate.