Qualifications
It all depends on what you want to do. If your goal in life is to become a lobbyist or a campaign manager, then you're best served by a master's degree in political science or a related field, like public administration or international relations. You'll pick up foundation courses in political theory and electives in a particular subtopic, like American politics or comparative politics.
Depending on what school you choose to attend, you may be required to complete a thesis…in which case, pick a topic that interests you and has some application to the career path you want to pursue.
You might also want to find some time in graduate school to complete an internship with the company, government entity, or non-profit organization you want to work for once you've earned your degree. A ton of people will be angling for the same job as you, and applicable work experience will help set you apart from the pack.
If your goal in life is to become a professor or a political science guru, then you're going to want a doctoral degree in political science. Yes, you'll lose years of your life to classes on methodology and research and learning how to teach undergraduates. Yes, you'll sob over your keyboard as you write a dissertation that became boring forty pages ago.
But, in the end, your PhD will give you access to positions at universities, think tanks, and in the government that simply are not available to political scientists with terminal master's degrees. Stock up on tissues and write that thesis.