I have little doubt that Trump was reasonably sincere in everything he said on the campaign trail. Even when he made contradictory promises minutes apart he was reasonably sincere each time. And if he had a magic wand he would do everything he promised. Poof, everyone would have health care that was better and costs less. Poof and a wall would appear on the border. Poof, all the coal miners would be back at work making tons of money mining coal at the same time as we had more natural gas from more fracking. Poof, ISIS is defeated. Poof, Poof, Poof, Poof, Poof.

But he's absolutely clueless about what it would take to create better health insurance or what it would cost. He has no idea what it would take to build a wall or if it would actually be successful if it were built. He has no idea how to put unemployed coal miners or any of the white men with only a high school diploma back to work. He has no secret plan to defeat ISIS, that was a lie, but he sincerely wants to defeat  them. He has few people in his cabinet that have the knowledge to create any plan to do any of these things. If he had people with the knowledge to create the plans Trump wouldn't read or understand them and would be incapable of bringing congress together to negotiate a compromise. I'm sure he sincerely wants to pass legislation that the American people would love so his poll numbers would go up. But he doesn't have the slightest idea how to get anything passed through congress.

So yes, I agree with you, Trump " was reasonably sincere in promising during the campaign." But what does that matter? Why should anyone care?