Mueller’s team is reportedly questioning whether Russian oligarchs illegally sent cash donations to Trump’s campaign or inauguration. In at least one instance, an oligarch was stopped upon entry to the United States and his electronic devices were searched.
While donations to Trump's campaign are reported to the Federal Election Commission and can be scrutinized by the public to some degree, no independent accounting has ever been made of the inauguration fundraising, which pulled in more than $107 million, an all-time record. Although Trump himself promised repeatedly that leftover inauguration funds would be donated and also to release a public accounting, no such information has actually ever been made available (details here).
CNN's reporting indicates that "Mueller’s team has intensified its focus into the potential flow of money from Russia into the US election." Any such foreign cash given to Trump's campaign, of course, would be illegal.
Reporting by Mother Jones last year revealed that "the head of the American subsidiary of a Russian conglomerate owned by a Russian oligarch with close ties to President Vladimir Putin made a huge donation" to the inaugural fund (details here).
It's curious how Trump repeatedly claims he has nothing to do with Russians yet more and more Russians are revealed from his past and present.
This revelations about the oligarchs being questioned strongly suggests Mueller's team knew a good bit before they were questioned. Federal investigators don't engage in fishing expeditions -- they ask questions when they know connections already exist.
This is a development that certainly bears watching for more news updates. Stay tuned.