There is information available to support the thesis that "Outcomes in American politics tend to serve the interests of the wealthy because poor people are less likely to vote." One source of information would be to compare the number of the wealthy people voting to the number of poor people voting. If more wealthy people are voting, it is a natural conclusion to draw that they are electing more wealthy people to office. Additionally, one could compare the number of wealthy people serving in government to the number of poorer people (middle or working class people) serving in government. If more wealthy people are elected, it is natural to conclude they would support the interests of the wealthy. Additionally, you could look at laws which are being passed to see if they are more likely to help the wealthy or the poor. If more wealthy people are voting and electing wealthy people, the laws which are passed should be favoring the interests of the wealthy. Finally, you could examine the rationale for those who favor voter identification laws (where you have to show identification to vote). Why is this an issue? Who tends to support passage of these laws? Why would they want these laws passed? What all of this shows is how important it is for people to vote. These are several examples of evidence which could be used to support the hypothetical thesis you mentioned.