Trump can make money the easy way by (a) selling stocks at a high price, (b) posting a "tweet" which will make the stock market go down immediately, (c) buying back those stocks at a lower price, (d) posting a tweet which will make the stock market go up again.
@helenS that is called insider trading, controlling the market, it is illegal. But SCOTUS said as longer as it is associated with his job, it isn't chargeable.