In a case that continues to have an enormous impact on elections at all levels of government, the court reversed decades of decisions by allowing corporate and union dollars to pay for ads and other campaign materials that urge voters to vote for or against a candidate for office. The 5-4 decision affected what are known as “independent expenditures.” Such funds are used by an outside party to pay for materials that favor or oppose a candidate, but the spending must be “independent” — the outside party isn’t allowed to coordinate it with the candidate. The decision led to the creation of super PACs — which accept unlimited donations and use the funds mostly on political advertising — and “dark money” organizations, nonprofits that do essentially the same thing but are not required to reveal their donors.