Answer:
Open Primary
Explanation:
One main characteristic of the open primary is that Voters do not have to be affiliated to a certain party in order to choose candidates from that party.
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We can see this in this part of the excerpt:
<em> . .. they get to decide on the day of the election if they are going to vote in the Republican or Democratic primary. . .</em>
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Since you can votes regardless of political affiliation, Open primary is the time where voters can choose based on their personal beliefs, preferred policies, or how the candidates' opinion on a certain issue.
This primary tend to attract the largest numbers of moderates and bipartisan. Who want to focus on the individual representatives rather than the whole party platform.