More detail on the topic https://fivethirtyeight.com/features/money-and-elections-a-complicated-love-story/

How strong is the association between campaign spending and political success? For House seats, more than 90 percent of candidates who spend the most win.

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Money is certainly strongly associated with political success. But, “I think where you have to change your thinking is that money causes winning,” said Richard Lau, professor of political science at Rutgers. “I think it’s more that winning attracts money.”

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Instead, he and Lau agreed, the strong raw association between raising the most cash and winning probably has more to do with big donors who can tell (based on polls or knowledge of the district or just gut-feeling woo-woo magic) that one candidate is more likely to win — and then they give that person all their money.

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Money matters a great deal in elections,” Bonica said. It’s just that, he believes, when scientists go looking for its impacts, they tend to look in the wrong places. If you focus on general elections, he said, your view is going to be obscured by the fact that 80 to 90 percent of congressional races have outcomes that are effectively predetermined by the district’s partisan makeup

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But in 2017, Bonica published a study that found, unlike in the general election, early fundraising strongly predicted who would win primary races. That matches up with other research suggesting that advertising can have a serious effect on how people vote if the candidate buying the ads is not already well-known and if the election at hand is less predetermined along partisan lines.

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Another example of where money might matter: Determining who is capable of running for elected office to begin with. Ongoing research from Alexander Fouirnaies, professor of public policy at the University of Chicago, suggests that, as it becomes normal for campaigns to spend higher and higher amounts, fewer people run and more of those who do are independently wealthy. In other words, the arms race of unnecessary campaign spending could help to enshrine power among the well-known and privileged.