What is the prerequisite for joining a political party

Generally, political parties are open to any individual who shares the values of that political party. Most political parties appreciate the support of everyone who is interested in getting involved.

And where the only condition that exists in the United States, - where any person can designate itself as belonging to a political party during the voting record-, is that the person is of legal age, is 18 years old, to be able to vote, and to be able to officially join any political party.