Nonetheless, Howell's 93-page order that required Miller to appear before the grand jury said: "multiple statutes authorize the Special Counsel's appointment, and the official who appointed the Special Counsel had power to do so".
That challenge was rejected, however, and U.S. District Chief Judge Beryl Howell on Friday found Miller in contempt but stayed the order pending appeal, the Post reported.
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But Mueller's subpoena of Miller and other Stone associates recently suggests he is now focusing on whether Stone may have had knowledge in advance about the damaging leaks of Democratic documents that Guccifer provided to Wikileaks in the months running up to the November 2016 presidential election.
Stone himself has not yet been questioned or subpoenaed in the investigation.
Paul Kamenar, the attorney for Stone associate Andrew Miller, whose refusal to appear before the grand jury Friday led him to be held in contempt, argued after the proceedings that Mueller's appointment is unconstitutional. Senate Majority Leader Mitch McConnell said he hopes to have President Donald Trump's nominee confirmed to replace retired Justice Anthony Kennedy before the new court session begins October 1. At least nine people associated with Stone have been contacted by the special counsel. The statement from lawyer Grant Smith said the exchange "provides no evidence of collaboration or collusion with Guccifer 2.0 or anyone else in the alleged hacking of the DNC emails".
In addition to Miller, John Kakanis, described as a personal assistant to Stone, along with social media expert Jason Sullivan, were subpoenaed by the special counsel over the spring.
The U.S. Senate intelligence panel, which is among several congressional committees conducting Russian Federation probes, is also investigating Wikileaks' role.