Can you be an economist with a political science degree?

For the most part, no, because degrees in political science lack a significant level of economics - or even quantitative - courses. It should be noted that, in many countries, being an 'economist' has no formal qualification, so technically anyone could claim to be an economist. However, again, if your question is: will a degree in political science prepare me for jobs requiring the skills of an economist, then the answer is no.