To become a consultant, you will have to develop a reputation for being accurate in your assessments. I think you should get involved in politics at the ground level - work on voter registration drives, join campaigns, etc., go to political functions. Much of politics is about networking. As to schooling, consultants tend to work with statistics, so I think you should gain a solid understanding of statistics. Beyond that, I'm not sure which way to go. There seems to be an element of marketing, and communications, tied to this position. I don't know if anyone offers a particular major in it. If not, you will need to design your own! Try to find successful political consultants in your area, and see if they will be willing to talk with you.
Sorry I was not of more help. Hopefully this has helped a little. Best of luck!
PS (for David)
I have not done much since retiring. I'm not truly a social person, and networking is extremely difficult for me. In my college days, I managed to get involved in party politics at the local level, getting selected to go to the senatorial convention from my local neighborhood precinct. I did block-walking and phone banks, and even painted banners for the convention (I doubt they do that anymore!) We formed a "Young Democrats" club on campus, and invited candidates to speak. We gathered signatures to help candidates get on the ballot. Once I became an officer, I used my knowledge and experience to help the police association, securing pay increases, training, and other things to improve morale and professionalism. Our little group (50 officers) went up against national unions who were trying to be the sole voice of employees. And prevailed! I really have not interacted much with consultants - I'm more of a sideline observer!
It's possible I misunderstood the question. I was thinking about campaign consultants. There is a whole different aspect, which would be more along the line of advisors. A possible position here would be the US Foreign Service, working at the embassies. It's extremely competitive to get in. The entrance exam is difficult. Somehow I failed the English section, even though I was an A/B student and did well on the ACT and GRE. If that is the direction you are going, I would strongly recommend learning grammar! It also tests your knowledge of world history, arts, culture, etc.
Whatever direction you are going, I would strongly encourage you to keep current in your technological skills and use of social media!