Robert Mueller
Andrew Harnik/AP Photo
In this June 21, 2017, file photo, former FBI Director Robert Mueller, the special counsel probing Russian interference in the 2016 election, departs Capitol Hill following a closed door meeting in Washington. President Donald Trump is questioning the impartiality of Mueller's investigation and says the probe is groundless, while raising doubts about whether a fired top FBI official kept personal memos outlining his interactions with Trump.