When do war chests deter?

I present a repeated election model of campaign fund-raising and spending where the incumbent may use money not spent in one election for a future election, i.e. may create a war chest. I characterize the conditions where an incumbent creates a war chest for deterrence. The strongest incumbents do not create the largest war chests since they deter the challenger on their own. It is the weaker incumbents who must create the larger war chests to deter the challenger.