Trump keeps campaigning, holding rallies, and is ever so concerned about the size of his inauguration crowd and approval ratings and phantom votes that cost him the popular vote...Why?

The obvious and simple explanation is that he's a narcissist that needs his ego constantly stroked. But what if there's an actual strategy here?

Trump's behaviour post election is unpresidented. All other presidents stop campaigning and stop worrying about the popular vote or polls for a while because they just got elected and they have shit to do. The election is over, now you need to govern, which means working with congress, not just tweeting at them to do something, but actually working with them, putting together bills that can pass, whipping votes, in essence the actual work of governing, using political capital, getting things done.

Trump doesn't know how to do that. He has a terrible relationship with the party, doesn't know how to work with congress, and his advisers are not exactly over-burdended with high-level experience. He CAN'T work the system, he doesn't know how and doesn't want to.

During the primaries he bullied the other candidates, he used his growing twitter army, his base of rabid supporters to both attack his opponents and keep the GOP in line. The GOP could have kept him from getting the nomination, could have treated him unfairly, like the DNC did to Bernie, but he had such a grip on his loyal followers that the GOP feared reprisal. Look at how many GOP politicians have fallen in line for fear of being singled out and attacked by his base.

Trump wants to keep that up. Trump wants his powerful and energetic base to be the leash for the GOP. The attack dogs he can unleash if a politician doesn't work with him.

In short, Trump is trying to keep the GOP in-line, and force them to work with him by keeping control of his rabid base. And he also needs there to be a perception that his base is huge and energetic -- enough so to be the biggest inauguration turnout in history. This is why he cares so much about perception and what CNN is talking about. He wants the GOP to know his base is huge and rabid so they won't mess with him... and if his approval ratings are shit and he lost the popular vote by 3 million and his inauguration was small and so on, then the GOP won't be kept in line by the fear of Trump's Almight Incredibly Numerous Team (or TAINT). Trump's energetic TAINT is what he expects to whip votes and make the GOP work with him. Without it he has no power over the GOP.