Citizens United v. FEC had a profound impact on which aspect of U.S. politics?

The case of Citizens United v. Federal Election Commission significantly altered the landscape of campaign finance regulations in the United States. In 2010, the Supreme Court ruled that corporations and unions could spend unlimited amounts of money on independent political expenditures, effectively equating these expenditures with free speech protected under the First Amendment. This landmark decision dismantled restrictions laid out in previous campaign finance laws, particularly those that limited the amount of money that corporations and unions could contribute to political campaigns.

The ruling allowed for the establishment and growth of Super PACs (Political Action Committees), which can raise and spend unlimited amounts of money to advocate for or against political candidates, provided they do not coordinate directly with the candidates' campaigns. This increased financial influence has changed the dynamics of political campaigning, leading to larger sums of money being funneled into elections, often overshadowing grassroots efforts and individual contributions.

While the other options touch on important aspects of American governance, they do not directly relate to the core implications of the Citizens United decision as it pertains specifically to the regulation of campaign financing and political speech. Therefore, the case's most profound impact lies firmly within the realm of campaign finance regulations.