So one of the open-source intel folks has tried to lay out what they think happened with this peace plan (and remember, Witkoff was not qualified to do this stuff from the beginning)
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It appears that somebody instructed Marco Rubio to go along with the story unfolding and it looks to me that this resulted from the following chain of events. I will lay it out here:
Everything points to the direction that Witkoff and Kirill Dmitriev were hammering out this 28 point surrender paper, without informing the US Secretary of State or the Ukrainian government. It contains primarily Russian wishes and unrealistic Russian demands, but Witkoff basically took them over in the list.
Kirill was then leaking this Russian wishlist to Axios, well-knowing what it is. Witkoff basically confirmed.
The intent followed two objectives. First, maximalist wishlist of the Russians should be engraved cognitively in media sphere for everyone before any pushback occurred. Two, it should test the US government how it would react to the backlash which will inevitably follow.
Rubio unaware of the contents of the talks was then confronted by a bipartisan group of US Senators and gave them his answer, which at this moment was truthful.
The senators then went public quoting Rubio: “It is not our recommendation, it is not our peace plan.”
At this point the US officials in the Trump administration must have started to realize that something is going wrong. As intended the leak totally blind-sided them. They completely lost control of the situation, but grudgingly decided to go along with it. Rubio was then compelled to go public and claim that it was indeed the plan, while watering down that it yet was just the Russian side, with some previous input from Ukrainian side.
This is my assumption based on facts I see so far.
This whole episode reveals that the current US negotiating team is completely out of its depth and that people involved in this "negotiation“ are absolute amateurs to say the least. Ukraine is well advised to push back hard and not leave any doubts that this surrender paper is dead in the water by countering it with a new peace proposal.