Imagine for a second that Trump is an agent of Putin (big stretch I know):

What could he possibly do that would be more destructive to the US than what he's doing right now?

People would jump to nuking stuff, but that isn't realistic. If trump gave an order right now to nuke Iran, I have a feeling that order would be disobeyed.

Putting people in charge of agencies they want to see shut down, then running them into the ground (EPA, FDA, Education, etc), forcing out all the veteran, knowledgable staff.

Then shut down the government indefinitely to get rid of more federal workers.

Already we are experiencing less secure airports from TSA agents calling in sick because they don't want to work for no money. And this shutdown has no end in sight, its just going to keep getting worse.

In addition, he attacks all of our longtime allies and alliances, while befriending all of the bad actors in the world. effectively severing a lot of our international influence.

It will take decades to undo all the damage Trump has done to our country. Just like Putin would want (If it was his idea, of course....)