Which Supreme Court case is considered a landmark ruling related to corporate campaign financing?

The landmark ruling related to corporate campaign financing is indeed Citizens United v. Federal Election Commission. This 2010 Supreme Court decision significantly changed the landscape of campaign finance in the United States by ruling that corporations and unions could spend unlimited amounts of money on political campaigns, as long as the expenditures were independent of the candidates' campaigns. This decision was rooted in the First Amendment, which protects free speech, leading to the conclusion that spending money to influence elections is a form of protected speech.

The ramifications of this ruling have been profound, as it permitted a surge in political spending by outside groups, often leading to concerns about the influence of money in politics and the potential undermining of the democratic process. This case highlighted the intersection of corporate interests and political power, reshaping how campaigns are funded and how political organizations operate in the U.S.

In comparison to the other options, Brown v. Board of Education deals with desegregation in public schools, Roe v. Wade focuses on abortion rights, and Miranda v. Arizona pertains to the rights of individuals in police custody. None of these cases address issues of campaign financing or corporate influence in politics, which is why Citizens United stands out as the relevant ruling in this context.