I think it depends on what you want to have left over when you’re done.
Smoking uninhabitable rubble? Roll out the nukes.
However, if you want to be the proverbial man on a white horse, to ride in and rescue the nation (from the trouble that you yourself caused), then you need to cause widespread fear and distrust among the citizens, so that they will voluntarily curtail their civil liberties for the sake of a putative safety. The main tactic should be random, destructive and scary terror attacks. Scapegoating and irrational targeting of certain groups and individuals will help create this atmosphere of suspicion and paranoia, and then will be fed by the attacks themselves.
Then you need to establish a “grass-roots” movement dedicated to traditional values and to purifying the nation. Questionable fringe-y value systems should be ridiculed and straw-manned to death. You don’t have to make much sense, just keep pounding at the talking points until they become generally accepted as at least valid, if not completely true.
You won’t actually need your whole billions to accomplish this, just some seed money to get it started. Most of your money will be spent on planning the terror attacks. You need to make sure they can’t be traced back to any group that you actually support, and they need to be both unpredictable and recognizable for what they are. These attacks should target the things that people already consider important - food, transportation, communication, entertainment, general comfort.
About this time you (or the empty suit that you are going to control) start to make a reputation, first locally, then nationally, as a charismatic, dynamic leader who can make sense of the chaos and take the country back to its root values. You (or he) will be an effective speaker, who doesn’t actually say much of substance but who definitely stands for what is right (whatever that is).
Finally, you need some climactic event, possibly an assassination, that is timed so as to sweep you into office with powers that make martial law look like anarchy. (Okay, I stole that line, but it fits.)