Hi Matthew - I definitely agree with Phi's answer. There are a large number of career possibilities if you major in political science as a undergraduate. I'm getting a PhD in political science (after receiving an undergraduate degree in public policy and international affairs). Usually, people who get a PhD in political science either go into:
1) academia: this means they become professors at universities who do research on politics and who teach classes related to politics
2) government / think tanks: this means they work for government agencies, international organizations, or think tanks as policy-maker and policy-advisors.
One thing to note is that getting a PhD in political science is a long term commitment (usually 5-7 years), and top PhD programs are very competitive (you have to have a strong undergraduate GPA, good letters of recommendations from your undergraduate professors, good GRE scores). But if you get in, instead of you paying tuition (which you have to do for undergraduate and masters programs), the PhD program pays you (usually your tuition, healthcare is free, and you get a stipend of around $30,000 per year).