Can money buy control of Congress?

Can a political party spend enough across electoral campaigns to garner a majority within the U.S. Congress? Prior research on campaign spending minimizes the importance of campaign heterogeneity and fails to aggregate effects across campaigns, rendering it unable to address this question. Instead, we tackle the question with a system-level analysis of campaign expenditures. First, using a flexible machine learning approach, we show that spending has substantial and nonlinear marginal effects on outcomes at the level of the campaign. Second, by aggregating these effects to the entire U.S. Congress, we show that large seat swings that change congressional control have, in the past, been possible for expenditure levels consonant with those presently observed after having removed the most extreme levels. However, this possibility appears to have faded over the past decade. Our approach also allows us to illustrate the often significant effects that eliminating campaign spending could have.