WASHINGTON _ Special counsel Robert Mueller served U.S. President Donald Trump's election campaign a subpoena in mid-October, according to two people familiar with the matter, in the latest sign that his criminal investigation is aggressively pursuing links between campaign officials and Russia.
The subpoena to more than a dozen campaign officials sought documents related to any contacts they had with Russian operatives, according to one of the people who requested anonymity to speak about sensitive investigative matters.
One of the people described the subpoena as relatively routine and an effort by Mueller to ensure his investigators have access to all the materials they have previously sought. Mueller requested some new supplemental materials but the subpoena doesn't represent opening a new line of investigation, this person said.
The other person, however, cautioned against interpreting the subpoena as a sign that Mueller isn't opening new components of the probe. The existence of the subpoena was reported earlier Thursday by The Wall Street Journal.
The revelation of the subpoena came on the same day that the top Republican and Democrat on the Senate Judiciary Committee pressed Jared Kushner, a senior White House adviser and Trump's son-in-law, to provide additional documents for its Russia investigation.
Judiciary Chairman Chuck Grassley and Democrat Dianne Feinstein wrote a letter Thursday to Kushner's lawyer, Abbe Lowell, saying that Kushner didn't turn over some documents first requested on Oct. 18, nor has he agreed to a transcribed interview. They said the documents include some related to his security clearance and his communications with former national security adviser Michael Flynn.
The letter said that "other parties" had given the committee documents concerning a "Russian backdoor overture and dinner invite" that Kushner also forwarded, but that Kushner hadn't sent a copy to the committee.
