NGS Style Manual‎ > ‎- P -‎ > ‎

POLITICAL PARTIES, party

Capitalize specific parties such as Communist, Democratic, Fascist, Labor, Liberal, Republican, Socialist:
  the Democratic Party, the party
a Democrat
Democratic platform
Democratic Convention, the convention

Republican Party, the party
a Republican
Republican platform
Republican Convention, the convention
Lowercase communist, fascist, liberal, socialist, etc., when reference is to a political philosophy and not to a party:
            republican principles, etc.

Capitalize Party with name of a political party:

but
Labor Party, the party
Labour Party (British)

Republican Party, the party
Communist Party, the party
            Liberal Party, the party
            the Liberals
            a Liberal (member of party)
            a liberal (general sense)