Why is spending money on political advertisements considered a form of expression?

In the context of the First Amendment, the U.S. Supreme Court established in Buckley v. Valeo (1976) that spending money is inextricably linked to political expression in a modern mass society.1

The court reasoned that virtually all effective methods of communicating political ideas—such as printing leaflets, holding rallies, or broadcasting messages—require the expenditure of funds. Because political campaigns rely heavily on mass media, the court concluded that limiting campaign expenditures imposes a direct and substantial restraint on the quantity and diversity of political speech. Consequently, the government cannot restrict such spending simply because it deems the promotion of certain political views to be excessive or unwise.1

This principle was further expanded in Citizens United v. Federal Election Commission (2010), where the court ruled that prohibiting corporations and unions from using general treasury funds for independent political advertising also violates the guarantee of freedom of speech. By enabling individuals and groups to buy advertisements or pool resources, spending is viewed as a necessary instrument for exercising the fundamental right to express political messages.23