So the next next President of the USA has just got in his position, and by electoral estimates and the power of the status quo maintenance, he knows that he will win his re-election, so he is sure that he will be in this position for the next 8 years.
But our President has a problem: he doesn't want to be a career politician, and so he wants to retire after his term. He has dreams he wants to pursue, and such dreams are costly. On the other hand, our President wants to make a lot of money using his presidential salary, investing in whatever profitable activity he can put his money to be use of, so whatever he wants to do, he must do it in this gap of 8 years. And on top of that, our President is someone who wants to be as righteous as possible, as he cares about his reputation and he cannot allow himself to do anything bad.
It's obvious that being a politician is to be inside a system that allows and sometimes even coerces the representatives of the people in doing bad acts, and that's why our President wants to do only the 2 presidential terms and then get out of it. To finish it, let's a put an "easy" mark here: 1 billion of dollars (or more if possible, maybe 10 billion, who knows).
Of course, we have some restrictions to limit our financial options, and these are the rules:
1. The President cannot receive money from illegal actions or dubious representatives. Our President is a man who cares about doing the right thing, and so he doesn't want to do anything that can harm his image or give potential ammunition to the opposition. Because of that, no money or service that came as a result of bribery, lobby or any kind of corruption will be accepted or expected. If our President receives any anonymous donation, he will investigate and, if he found that it came from an illegal or bad source, he will return the money and report it to the responsible authorities.
2. The President cannot be director, chief, manager or hold any corporate title, and he also cannot found or manage a company. It's obvious that, if our President has any high position in a company, any political action that could change the economical environment would be criticized as a "one-sided" or "biased" action that has the growth of his own capital as a goal. In fact, it's even illegal in some countries. A warning here: can our President be an anonymous investor in a company? I sincerely don't know. Is it illegal, or is it bad for his reputation? I guess that is the rule that could be the most discussed, because it's the rule that stands most in the "gray area".
3. The President cannot engage in illegal activities. The President wants money, but not a criminal record. Slave trade, trading weapons or uranium in the black market, selling federal secrets to other governments, ... that's all activities that our President will not do.
4. The President cannot engage in activities that are not compatible with his presidential activities or that could go beyond his available time. The President is, you guessed it, the President, and so he must work, because he has political things to do and a country to worry about. Because of that, his economical activities must be possible to be executed in his spare time. He cannot spend the entire day checking the ups and downs of his assets in the stock exchange.
P.S.: After writing all of these laws, I guess that the second one is the hardest to have an absolute position about it. The President could have a lot of stocks, which are anonymously in his hand. If such a thing was discovered, how bad would that be to his reputation?
On the other hand, let's say that the President has invested in Bitcoins. He could openly tell that to the public, and even create laws to make it more accessible to the people to invest in it. Such action would be criticized by some, but would it be bad for his image? Or maybe not that bad, because it doesn't affect him directly, although he has a relation with it as an investor. Any clue or discussion about that would be very welcomed.
In short: how could a President become a billionaire without doing anything illegal, and using only his salary?