Start with the whole pie. The total cost of U.S. federal elections — every dollar spent by candidates, parties, and outside groups combined — was about $3.1 billion in 2000. By 2012 it had roughly doubled to $6.3 billion; by 2024 it reached $14.8 billion. The most expensive cycle on record is still 2020, at $15.1 billion — more than the 2000, 2004, and 2008 presidential cycles put together.
Not all of that growth is Citizens United. Campaigns got more competitive, presidential self-funding rose, and online small-dollar fundraising (ActBlue, WinRed) brought in millions of new donors. And some of the increase is simply inflation: adjusted into constant 2024 dollars, the 2020 cycle ($18.3 billion) was far more expensive than 2024 ($14.8 billion), and the 2000 cycle's $3.1 billion is about $5.6 billion in today's money. Even after stripping inflation out, though, the real cost of elections has roughly tripled since 2000 — and the steepest acceleration lines up with the maturation of the super PAC and outside-money machinery the decision set loose. The rest of this report zooms into that machinery.
(The sawtooth pattern is normal: presidential cycles cost far more than the midterms between them.)