Final answer:
America may be struggling most with the principle of Responsibilities & Duties of Democratic Citizenship, particularly in terms of voter participation. Limited voter turnout reflects a lack of engagement that undermines the majority's ability to influence governance.
Step-by-step explanation:
The key principle of democracy that America is struggling with the most could arguably be F) Responsibilities & Duties of Democratic Citizenship, particularly regarding voter participation. The core concept of a democratic government is predicated on active civic engagement and the actualization of the right to vote. Despite the gravitas of Lincoln's phrase "of the people, by the people, for the people", which encapsulates the essence of democracy, there remains a significant portion of the American electorate that does not participate in elections.
Limited voter turnout suggests a detachment from civic responsibilities, which in turn undermines the democratic principle of governance by the majority's will. A variety of social issues influence this political participation, including but not limited to socio-economic factors, political alienation, and a lack of faith in the political system. Addressing these issues is essential to strengthening the democratic process and ensuring that it is reflective and inclusive of all citizens' voices.