Media outlets are always looking for experts to provide insight and context to breaking or trending news stories. The good news is that if you have done step one - written a book - you will already be considered a subject matter expert.
Besides writing a book, your professional background should lend you political or governmental expertise. Ideally you will have worked in government.
Maybe you were chief of staff at the mayor's office, or the governor's political director. A city council member, former judge, assistant district attorney, policy advisor, even a city clerk - these are all roles that have enriched your perspective as a government insider. Whether it is at the local, state or federal level, you have an understanding of the inner workings of government that most people do not. This makes you an expert.