Final answer:
American political parties often fail to fulfill the responsible party model due to a lack of distinct visions, difficulty in enacting reforms, and an increase in candidate-centered campaigns that reduce party influence.
Step-by-step explanation:
The American political parties struggle to fulfill the terms of the responsible party model as they often fail to offer clear, distinct visions for the country's future and struggle to enact major reforms when elected. This results in ambiguity and voter confusion regarding who should be held accountable for governance outcomes.
Factors such as divided government, partisan polarization, and the rise of candidate-centered campaigns, which emphasize individual candidates over party platforms, further diminish the effectiveness of parties in fulfilling their roles. The decline in party's mobilization power has led to candidates themselves filling the power vacuum, as seen in the case studies of Ross Perot and Donald Trump.
Moreover, the complexity of political differences across the nation creates a challenge for maintaining coherent and consistent party positions that can appeal to a broad coalition of voters without becoming too diluted or leading to internal disagreements.