Why have U.S. presidential candidates come to personify their political parties?

In the context of U.S. sociology and political science, the personification of political parties by presidential candidates is largely a result of the shift toward candidate-centered elections.1

Historically, American political parties were decentralized, loose alliances of state and local organizations lacking rigid national hierarchies. Because these parties often functioned as "pseudo-two-party systems" with shifting coalitions rather than disciplined ideological blocs, they struggled to maintain consistent national unity.12

Several factors have driven the transition toward candidate-centered politics:

• Weakened Party Control: The decline of traditional "party bosses" and the rise of primary elections have allowed candidates to bypass traditional party organizations to secure nominations.13
• Individual Campaigning: Modern elections are heavily focused on the individual candidate's appeal, talent, and ability to raise funds, rather than relying solely on the party apparatus.1
• Presidential Leadership: Because national party organizations are often weak between elections, the president (or the party's presidential nominee) serves as the primary source of cohesion for the party, effectively becoming its face and leader.2

Consequently, voters often look to the candidate as the clearest indicator of a party's political orientation, as individual platforms are frequently synthesized into the candidate's persona.4