I see your point, but I also see its short-sightedness. Nobody "sucks cock" for no reason, especially in politics.

Source 01: It's recent, I didn't have that. All I read is that he doesn't want the conflict to escalate even more, and I think we'll all agree on not wanting a 3rd world war/nuclear apocalypse. So far, it is coherent with his positions, and I agree that it would only benefit America (who's already led by a fascist and holding Europe by the energetic balls after the destruction of the Northstream pipeline). Russia has threatened to use nukes, after all. Also, if Russia is gaining resources and a power stance against NATO by invading Ukraine, Ukraine is gaining nothing by pushing the front on Russia, except revenge. It'd be cool if they could off Putin and end this madness (they have tried by sending attack drones), but if it could be done, it would already have been done, I guess. Also, Putin had told in the past that if NATO, that he considers to be an American-led adversary, tried to integrate Ukraine, making it an "American" advanced base just next to Russia, the shit would hit the fan, and it happened. IMHO, if Ukraine could have been an independent, buffer state between Russia and NATO states, or maybe an exchange state (commercial, diplomatic, etc), things may have not become as dire as they are right now (except, Russia has already invaded and claimed Ukrainian territory in the past).

Source 02: I don't trust Think Tanks. They're never neutral and are usually composed of university people with no professional outcome other than lending their voices to the private interests that pay them. I'll agree on one thing, though: how the fuck could Ukraine organize presidential elections in its current state (unless there is an actual ceasefire), and even if there was a ceasefire and an election, what would guarantee that those elections wouldn't be manipulated by Russia and that a Russian plant wouldn't be elected?

My speculation: Trump isn't eternal. Putin either. But, to preserve France independence from the predatory, failing and now fascist USA (which will not end with Trump) in the long term, France needs to get cheap Russian energy (Northstream), instead of being forced to buy American energy at an arm's cost. I think the shift Mélenchon is planning for is simply the fall of the USA, which will make Europe even more vulnerable to Russia's wrath. And in a world where the USA has destroyed itself, the needed allies are... Russia and China, because America isn't top dog anymore. I think Mélenchon is pushing for an end of the war even if that would benefit Russia (which isn't fair for Ukraine), in order to escape the predation of the USA, but I don't think he'd suck Putin just for the sake of sucking Putin's cock. There isn't even an ideological similarity between the two of them. Russia isn't a leftist state. Russia is just the predator that is the closest, and the failing USA will not defend Europe (which has been made even more blatant by their Iranian clusterfuck) as it has pushed for not supporting Ukraine anymore. If there is a Russian plant in the western world, it's Trump. It's Trump who has summoned Zelensky to humiliate him publicly and pushed him to surrender to Russia. Not Mélenchon, who isn't even in power. Trump is the pivot point. Trump is the Russian asset.