Mueller's team has been asking about a convention-related event attended by both Russia's U.S. ambassador and Jeff Sessions, the first U.S. senator to support Trump and now his attorney general, said one source, who requested anonymity due to the ongoing investigation.
Another issue Mueller's team has been asking about is how and why Republican Party platform language hostile to Russia was deleted from a section of the document related to Ukraine, said another source who also requested anonymity.
Investigators have asked detailed questions about conversations that Sessions, then a Trump campaign adviser, had at a convention event attended by then-Russian Ambassador to the United States Sergei Kislyak, said the first source, who was questioned by Mueller about the event.
The same source said
Mueller's team also has been asking whether Sessions had private discussions with Kislyak on the sidelines of a campaign speech Trump gave at Washington's Mayflower Hotel in April 2016.