What was the key outcome of the Citizens United ruling by the US Supreme Court?

The Citizens United ruling by the US Supreme Court is fundamentally significant because it established that corporations and other organizations can spend unlimited amounts of money to support political causes and candidates. This decision revolves around the interpretation of the First Amendment, which protects free speech, and the Court concluded that spending money in support of political speech is a form of that protected speech.

The ruling allows corporations and associations to engage actively in the political process through independent expenditures, meaning they can spend as much as they wish to promote or attack political candidates, provided that these expenditures are not made in coordination with a candidate's campaign. This has led to a dramatic shift in political campaign financing, where the influence of money in politics has become increasingly pronounced.

In contrast, the other options do not reflect the core outcome of the decision. Corporations were already allowed to engage in political activities before the ruling, so the first option is inaccurate. The notion of political spending being taxed is unrelated to the Citizens United case, as the ruling does not address taxation of political spending. Lastly, while there are discussions and regulations around disclosure of political donations, the ruling itself did not mandate that corporations must disclose all political donations; rather, it focused on spending and not direct contributions to campaigns.