This is a good question. Foucault's theories of power and knowledge can indeed be applied to political power. In fact, it can be applied to pretty much anything that has power dynamics. Let me offer you one of his most often quoted sentences from this book, Power and Knowledge, to give you a sense of what he is trying to say about power and how it could be related to politics and many other areas.
"Each society has its régime of truth, its ‘general politics’ of truth: that is, the types of discourses which it accepts and makes function as truth; the mechanisms and instances which enable one to distinguish true and false statements, the means by which each is sanctioned; the techniques and procedures accorded value in the acquisition of truth; the status of those who are charged with saying what counts as true."
Based on this quote, we can say that those with political power by virtue of their power create "truth" in a sense. Therefore, if someone dissents, then they say that person is out of line or possibly even crazy, because those with power have already established their "general politics of truth." They have their own experts, their own specialists, their own worldview and they make all of this seem normative.
Let me give you an example, if you listen to the discourse of radical democrats, they will basically say that their ways are the only right way and if you disagree with them, then you are unreasonable. The radical republicans will say the same thing as well. Both are exerting their political power to create a social reality.