Longtime Republican operative and former Trump campaign adviser Roger Stone predicts special counsel Robert Mueller will indict Donald Trump Jr. on a "process crime."

“The special counsel is going to charge Donald Trump Jr. with lying to the FBI. Notice they’re not charging him for having an illegal meeting with a Russian at Trump Tower because there’s nothing illegal about that meeting,” Stone told James Miller of The Political Insider.

“[P]ut more precisely, the only thing illegal about that meeting was how the woman got in the country, how she got a visa from the Obama State Department, and why she was meeting with an official from Fusion GPS before and after the Trump Tower meeting.”

Stone is not the first former Trump adviser to predict legal trouble for Trump, Jr. Steve Bannon was quoted in January, in Michael Wolff's book Fire and Fury: Inside the Trump White House, saying, "The three senior guys in the campaign thought it was a good idea to meet with a foreign government inside Trump Tower in the conference room on the 25th floor - with no lawyers. They didn't have any lawyers."

EXCLUSIVE: Roger Stone, Robert Mueller's Next Target, speaks with The Political Insider

"Even if you thought that this was not treasonous, or unpatriotic, or bad shit, and I happen to think it's all of that, you should have called the FBI immediately."

When an intermediary proposed the meeting, saying the Russians were offering damaging information about Clinton, Trump Jr. responded in an email, "I love it."

Bannon was incredulous about the meeting shortly after it was revealed, according to the book, concluding sarcastically, "That's the brain trust they had."

"They’re going to crack Don Junior like an egg on national TV," added Bannon.

An associate of Stone was found in contempt on Friday on August 10 after refusing to appear as a witness before a grand jury convened as part of Mueller's Russia probe, U.S. media reported.

Andrew Miller's refusal to comply with the subpoena from Mueller's office prompted a sealed hearing before a federal judge, who then made the ruling, the Washington Post and CNN reported.

In a related development, another Stone associate, comedian and talk show host Randy Credico confirmed that he had been subpoenaed by the special counsel's office, which is probing alleged Russian interference in the 2016 U.S. presidential election.

Credico told Reuters that he had been summoned to testify before a grand jury on September 7. CNN first reported the subpoena.

CNN also reported that Kristin Davis, another Stone ally and one-time Manhattan madam, was scheduled to appear before the grand jury on Friday.

The latest witnesses in Mueller's probe appear to suggest it is focusing at least in part on Stone, an early Trump backer with a reputation as an aggressive political operative.

Russia has denied any meddling in the election. Trump has repeatedly said there was no collusion between his campaign and Russia and has called Mueller's investigation a witch hunt.

Stone, who has denied any wrongdoing, has previously said that eight of his associates have been contacted by Mueller but that the special counsel's team has not contacted him.

Mueller issued a subpoena to Miller earlier this year, making him the third Stone associate to be identified as having been contacted by Mueller's investigators.

Miller's lawyer had sought to quash the subpoena.

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.

Jason Sullivan, a social media expert who worked with Stone, has testified to the grand jury. John Kakanis, an assistant and driver for Stone, has also been subpoenaed.

Mueller's outreach may mean he is focusing in part on whether Stone may have had advance knowledge of material detrimental to Trump's 2016 Democratic opponent Hillary Clinton that U.S. intelligence agencies have concluded was obtained by Russia through hacking.

The U.S. Senate intelligence panel, which is among several congressional committees conducting Russia probes, is also investigating Wikileaks' role