Why did Buckley v. Valeo allow limits on direct contributions to political candidates?

In the landmark case Buckley v. Valeo (1976), the U.S. Supreme Court upheld limits on direct contributions to political candidates because it identified a compelling governmental interest in preventing corruption or the appearance of corruption.12

While the Court acknowledged that contribution limits do impair First Amendment freedoms—specifically the right of association—it concluded that these restraints were only marginal. This is because contributors remain free to engage in political activity through other means, such as independent spending or associating with candidates in ways that do not involve direct financial contributions.1

Furthermore, the Court reasoned that when a contribution is made, the actual political speech is performed by the candidate rather than the contributor. Consequently, the government’s interest in maintaining the integrity of the democratic process by limiting the potential for a quid pro quo—an exchange of political influence for financial benefit—outweighed the limited impact on the contributor's freedom of expression.123