There's a large empirical literature on the issue and the conclusion is that money is more or less irrelevant in politics. Political campaigns are entirely ineffective.
The Minimal Persuasive Effects of Campaign Contact in General Elections: Evidence from 49 Field Experiments [0]
"First, a systematic meta-analysis of 40 field experiments estimates an average effect of zero in general elections. Second, we present nine original field experiments that increase the statistical evidence in the literature about the persuasive effects of personal contact 10-fold. These experiments’ average effect is also zero."
Does Money Buy Votes? The Case of Self-Financed Gubernatorial Candidates, 1998–2008 [1]
"The apparent effect of spending on votes is severely inflated by omitted variable bias: the best candidates also happen to be the best fundraisers. [...] self-financed spending has no statistical effect on election results"
[0] https://papers.ssrn.com/sol3/papers.cfm?abstract_id=3042867
[1] https://link.springer.com/article/10.1007/s11109-012-9193-1