At the core of the court's decision was the longstanding concept that corporations are "people" under the law, entitled to many of the same constitutional rights granted to natural persons. Many speech advocates believe eliminating McCain-Feingold's limitation on campaign speech was the only logical application of that principle.
The immediate impact of Citizens United will be that corporations will not run afoul of the law if they pay for ads, books, movies or other media that could be interpreted as advocating for a specific candidate. The decision also eliminates the distinction between media companies and other corporations that have an interest in supporting or opposing candidates. (McCain-Feingold has always permitted newspapers, for instance, to endorse candidates.) This is particularly crucial for advocacy groups such as Citizens United whose sole mission is to influence politics, as well as non-profit, nonshareholder corporations such as the Chamber of Commerce and the Business Roundtable.
Regardless of its ultimate impact, Citizens United has received widespread attention, much of it negative. A February Washington Post/ABC News poll found that about 80 percent of Americans opposed the decision. This has sparked congressmen to propose new laws that would reverse or limit the impact of the decision. Even President Obama chimed in, promising a "forceful response."