Why Isn't Marco Rubio In Moscow?

 CBS News and other news organizations are reporting:

Steve Witkoff, President Trump's special envoy for Russia and Ukraine, has arrived in Moscow to discuss a proposed 30-day ceasefire between Russia and Ukraine.

Given that this is a high profile negotiation and one that Pres. Trump assured us wouldn't take but 24 hours to resolve, why isn't Secretary of State Marco Rubio in Moscow as the head of our negotiating team?

After all, he was the lead diplomat in Saudi Arabia when meeting with the Ukrainians last week. So he of course has first hand knowledge of the agreements and discussions and to my mind would have more cachet with the Russians than Mr. Witkoff.

And, since the Saudis were the actual parties mediating the negotiations between the Ukraine and the United States, why aren't they in a similar role here? It might not be that bad an idea to have a third party nation involved given the rumors around Trump's affection/admiration for Putin.