That's only part of it. With Trump has has a pliable fool to get what he wants. Russia doesn't need Exxon-Mobile to get that oil as there are other companies that could help them get that oil. Just they paid the most to him for the contract. Why else would Trump in one of the first things he did was eliminate oil companies from having to declare who they bribed in foreign countries to get contracts. Putin can get so much more from Trump.
Condi Rice and Robert Gates recommended EXXON's CEO Rex Tillerson to Trump - both Rice and Gates are EXXON consultants and carry weight in Repub circles.
Rex Tillerson's Company, Exxon, Has Billions at Stake Over Sanctions ...
But how, and why? It was reported when he was nominated for the SoS job that he planned to sell all his Exxon stock, which apparently was his only equity, and buy treasuries.