For the price of the Iraq War, we could make every vote for the right candidate in a swing state worth $10,000 according to philosopher Derek Parfit's calculations in Reasons and Persons.
Chapter 3 of Reasons and Persons, "Five Mistakes in Moral Mathematics", contains the section "Ignoring Very Small Chances". In it, Parfit cites academic research suggesting that the likelihood of an individual vote in a swing state deciding a presidential election is 1 in 100 million. Parfit argues that voting is still rational for those who have concern for others, despite the low likelihood of deciding the election.
If the difference between the policies of the better and worse presidential candidate is $1 trillion when added up across everyone, the 1 in 100 million chance of deciding the election divides out to a value of $10,000 to everyone. Despite the tiny chance of deciding the election, the tremendous value of a better president makes voting rational for those who care about others. Making every vote have a value of $1 trillion comes to $2 trillion less than Joseph Stiglitz and Linda Bilmes' estimate of $3 trillion for the total cost of the Iraq War.