Maybe he first wants to destroy the concept of truth

that's what authoritarian asshats do, usually early

Narcissism/megalomania/etc. eh!
The reality seems to be is that trump is dangerous, and that is what seems to be so important to focus on.
For perspective context, trump does seem to make 'El Duce' look a little moderate.
We 'all' need to deal with that. Make our proven system of checks and balances work. We survived the slavemasters civil war, powerful jim crow, robber baron capitalism and it continuing resurgences, various hate driven movements. Each of those 'survivals' took great effort and democracy oriented responses. As a nation we know this. Great efforts can prevail here.

Simple?

Destabilizing western alliances is advantageous to the dictater, who has already amassed an incredible fortune and wants more. Putin literally wants to dominate the world. Getting the American president to destroy not just America but the rest of the western world is part of Putin's goal.

And now Donald is trotting to Singapore to do Putin's bidding there.

...and self-promotion and self-aggrandizement.