(CNN) Roger Stone has beefed up his legal team, adding First Amendment and constitutional law expert Bruce Rogow to his roster of attorneys.

Grant Smith, another of Stone's attorneys, confirmed the expansion, which was first reported by ABC News.

"Mr. Rogow joined our team in April 2018 to defend a defamation suit here in South Florida. Because of his unmatched expertise and his superlative national reputation in Constitutional law, criminal law, and investigations, he has transitioned into the lead counsel role on these matters," Smith said in a statement. "Robert Buschel and I welcome the presence of someone with Mr. Rogow's stature and gravitas."

Stone's move to bolster his legal team comes as special counsel Robert Mueller has been circling President Donald Trump's longtime political adviser. Nearly a dozen of Stone's current and former associates have been summoned by Mueller's team for interviews or testimony before the grand jury.

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