It's plausible, but there are many ways to explain the status quo. And maybe all those are in play at once?

Russia would absolutely use and abuse any US political puppet they can get their hands on. After all, there's no point in getting into a shooting war with another nuclear power^1^. History has also shown that the USA united and moving in one direction at once is a force to be reckoned with. From Russia's perspective, it's way more economical to have your adversaries rip themselves apart for you. As the USA has had some pretty deep divisions since the Civil War, we are a clear target for this kind of strategy; we are already primed to disagree on things. The only real work to do is escalate the matter, and politics is a great lever for that. But I'll assert that there's no endgame necessary for this strategy: all they have to do is keep fueling chaos, keep the electorate divided, and keep everyone arguing while ignoring any common ground. From there, continued governmental dysfunction keeps us from being a bigger economical or political threat to others in the meantime.

That said, it's all conjecture. Let me take a less conspiratorial look for a second.

At the same time, it's cold comfort that some invisible hand is fomenting unrest and causing our biggest problems, rather than it being an inherently American dysfunction; classic self-coping denial. A bit like blaming your partner for why the relationship is in shambles, when everyone really needs to go to therapy and work on some root problems. Perhaps those causes are intractable, but as far as I can tell, nobody's working that out and focusing a lot of energy on wedge topics (symptoms, grievances) instead.

Edit: I am in no way implying that we need to validate all the obvious bad takes from the right wing. Far from it; call that shit out. Instead, I think it's crucial to look to how/why those takes get traction and focus there instead.

^1^ - proxy wars are weirdly okay, and have been for a long time. I'm still trying to figure that one out.