How does the structure of political party organizations impact candidates in elections and the legislature? How does the position of candidates within the party affect their success? To address these questions in my dissertation, I use social network analysis to study candidates’ relationships and the context around those relationships. I measure party networks with campaign finance transactions in seven states for the 2010 and 2012 state legislative elections. After a case study of Texas parties that establishes the validity of my approach, I compare the structure of party networks across states. Although I discover that these networks are relatively sparse in general, my results also reveal that parties in states with competitive legislative chambers tend to be more connected. Finally, I explore how the party structure influences candidates. By drawing upon Ronald S. Burt’s (1992, 2005) structural holes theory, I identify influential actors and examine how their network position impacts their success in legislatures. I find that influential candidates in the electoral party network are more likely to become a legislative leader in the following session, demonstrating an important link between electoral and legislative politics.