President Donald Trump unloaded Friday on Twitter on deputy attorney general Rod Rosenstein

He complained that he was being investigated 'by the man who told me to fire the FBI Director!'

Rosenstein tapped former FBI Director Robert Mueller to head a probe of Russian election interference

There is now a report that Rosenstein acknowledged he might have to recuse himself from overseeing the investigation because he could be a witness

The Washington Post this week reported that Mueller was also probing obstruction of justice – something Trump appeared to confirm  

Mueller has asked Trump transition officials to preserve documents that might be of interest to Russia investigators

Documents related to Trump-linked figures Paul Manafort, Mike Flynn, Carter Page, and Roger Stone sought