Here is more from Vanity Fair:
Mueller’s team has stopped two Russian oligarchs who recently made trips to the United States, searching at least one, and has made an informal overture to a third requesting an interview and documents, CNN reported Wednesday. According to multiple sources familiar with Mueller’s tactics, the special counsel is focused on the potential flow of money from Russia to Trump’s campaign and inauguration. He’s particularly interested in Russian investments in think tanks and political-action committees that donated to Trump’s campaign, and in “straw donors,” or American citizens who fielded Russian money to skirt campaign finance laws.
Here is a previous Think Tank Watch piece entitled "Mueller Probe Witness Linked to Shady Think Tank Payments," which discusses how United Arab Emirates (UAE) money circuitously made its way to a couple of Washington think tanks.