There are lots of possibilities.

One being mere FUD - remember that he doesn’t have to succeed to cause disruption, and even the attempt will draw focus away from Russia’s own annexation of Ukraine.

And if that can simultaneously be accomplished while also acting to isolate the USA away from its allies - and perhaps more importantly them away from the USA - then so much the better (for Russia I mean, though at the expense of the Western nations).

Or Putin could have meant it as a jest, and Trump did not realize that.😜

But I also think there’s a halfway decent chance that Trump himself won’t even bother trying - he could back down, and then claim: “see how reasonable I am, I wanted to do this crazy thing, but you didn’t want me to so I didn’t, yet now I want to do this other much more ‘reasonable’ thing and it’s my turn to win so you gotta let me have this new thing I want, if you want me in return to keep doing things your way occasionally, that’s called ‘compromise’ btw” (it’s actually not btw, as a better term would be rather “shifting the goalposts”, but whatever…).

And if that was the case, then we wasted all of our efforts trying to understand the “strategy” behind something that was only ever meant as a distraction to begin with - unless that’s what they WANT us to think, and then they push it through and actually get it DONE!? That’s the thing when facing against an opponent who actually knows what the word “strategy” means - whereas the voting public seems to have no clue, which is why we probably should not have been in charge in the first place 😞 (at least I heard that sentiment a lot after Brexit, by people in the UK - like “whoopsie, can we get a do-over?!” then doing the identical thing again every single time that the latter was granted, proving just how impossible it is to help people who are absolutely dead set against receiving that aid).

Also, bold of you to presume that the USA will ever have another election again… - it is now legal to assassinate his opponent if he so chooses, so the playing field has changed entirely. Probably he’ll allow bad candidates to run that have no chance of actually winning, so it will appear as if his preferred choice had won entirely legally (Jared Kushner? or some other handpicked candidate - in all likelihood by Putin, or whoever succeeds him and inherits whatever other dirt he keeps on all rich and powerful people around the world). The gloves are off now: this is a brave new world.