Campaign spending has diminishing marginal returns: past making a voter aware of a candidate or an issue, it doesn’t do much. It’s not the decisive factor in a partisan, general election, where party affiliation & incumbency matter more. The relation between campaign finances & election outcomes is correlation rather than causation. Donors contribute to candidates likelier to win, and wealthy donors contribute large sums to improve their access to the winner.

In major elections where the voters already know the candidates pretty well, advertisement money is mostly wasted. An advertisement is unlikely to cause a voter to flip parties.

Money matters more in primary races & local elections full of unknown candidates lacking an incumbent. There, ads help raise awareness of candidates & issues voters hadn’t known about. Multiple candidates of the same party may run, so party affiliation isn’t decisive, and advertising matters more.