One of the truisms in American politics has been that "divisive" primaries hurt the party's prospects of winning the presidency in the general election. However, traditional definitions of divisive primaries focus too much on candidate behavior and not enough on the actual divisions and fractures within a party. The Invisible Hands of Political Parties in Presidential Elections proposes a new measure of party cohesion that instead looks at individual donors who are willing to contribute to multiple candidates during the early stages of the presidential primaries. The authors of this collection reveal how these preprimary donor networks can serve as an accurate barometer of party unity, providing a significant perspective on the changing roles of political parties in American government today.