You can make deals with narcissists. You just have to frame them correctly. At no point, in the lifetime of the deal, should it be in their interest to renege on it. This gets more complex when other players are involved.

The problem with Trump is that he is like a toddler. They want the payoff straight away. As soon as has have this, however, the deal is effectively over. The trick would be to drip feed him the benefits, both financial and personal.