It's far simpler than that. In order to look good domestically Trump needs a foe, and China conveniently provides that foe. They're a credible threat, they are not his Russian buddies and the US is to a large extent dependent on them.
On top of that I suspect that when the last stone is overturned we will find a bunch of ways in which the US president and his cronies profited from the wild gyrations of the stock market as a result of the trade war.
No matter who's in charge in each moment, the West should try to convince China that it must transition to a political system like ours if they want to keep dealing with us.
Allowing China to maintain its tyrannic regime is extremely dangerous for everybody in the long run.
The change doesn't need to be abrupt and it's possible to make some assurances for people currently in power.
"Enforced" is not the word I was looking for. More like showing the ruling class that it's in their own interest to gradually apply some changes. There are many obstacles for such a strategy. But even if there isn't a clear path, there needs to be some factors in place for somebody inside to invent that path. If nothing is ever done, nothing will change.
That's the theory. The practice is the rulers will use the sanctions to prove to their people that the outside world is mean and evil and their only hope lies in their dear leaders.
On top of that I suspect that when the last stone is overturned we will find a bunch of ways in which the US president and his cronies profited from the wild gyrations of the stock market as a result of the trade war.