To keep the analogy true; the decision always was hers so the father has the choice of a) being honest and giving her the truth that will ring in her ears after her marriage has fallen apart or b) feeding her delusion by giving her an answer that makes everybody feel good for the moment.
If the father does a) she might actually listen to him but if not she will know when it's all over that he was a rock and she can trust his wisdom. If daddy does b) she will learn that his advice is just weak-kneed nonsense said to make her feel good and keep him safe from her criticism.
The your analogy assumes she might not marry one of the two you don’t approve of. That is not gonna happen. The USA will elect one of the two. So which one OF THE TWO would you prefer for the next 4 years? You can wish for some other option but it isn’t there.