https://www.sciencedirect.com/science/article/abs/pii/S02613...

https://www.researchgate.net/publication/240633007_Measuring...

TL;DR: Spending might matter up to a certain point, but becomes very inefficient. It's also more effective for challenges than incumbents.

https://en.wikipedia.org/wiki/Fundraising_in_the_2024_United...

https://en.wikipedia.org/wiki/Fundraising_in_the_2020_United...

https://www.washingtonpost.com/graphics/politics/2016-electi...