In a campaign spending contest model, this paper investigates whether the sources of incumbency advantage are able to generate the observed pattern of campaign spending and incumbent reelection rates in US elections and assesses the degree to which campaign finance reform can mitigate the negative repercussions of incumbency advantage. The paper extends the existing literature by allowing the electoral benefit to the candidate’s visibility to be stochastic which is intuitively appealing since one dollar of extra spending should not take a candidate from a certain loser to a certain winner. Officeholders’ ability to generate free media exposure alone is shown to be unable to match empirical regularities. Incumbent’s superior fundraising efficiency is the key to matching the observed patterns. In contrast to previous literature, the model predicts that campaign finance legislation can help reduce the challenger scare-off effect of incumbency advantage.