Former Trump campaign staffer Sam Nunberg’s meltdown on cable TV Monday triggered concerns for his mental health, and perhaps showed the stresses associated with being under a special counsel investigation.

But he also gave a sign of where Robert Mueller’s probe into Russian influence on the U.S. election might go next: longtime Trump ally and Republican operative Roger Stone.

Nunberg appeared to confirm as much in an interview on MSNBC. “I’m not going to cooperate when they want me to come in to a grand jury for them to insinuate that Roger Stone was colluding with [WikiLeaks founder] Julian Assange. Roger is my mentor. Roger is like family,” he said.

Stone, who worked officially on the Trump campaign only briefly, has so far remained unscathed by the probe despite the appearance that he had prior knowledge of WikiLeaks’ plan to release hacked Democratic emails in 2016. But there are mounting signs that Stone is in Mueller’s crosshairs.

A subpoena from the special counsel’s office leaked to Axios over the weekend shows investigators asked Nunberg for all of his communications with a long list of Trump officials, including Roger Stone. Last week, The Atlantic published previously private Twitter messages between Stone and WikiLeaks from October 2016, right after WikiLeaks released a trove of hacked Democratic emails and three months after U.S. intelligence officials announced foreign spies were behind that hack.

WikiLeaks has denied the group ever had contact with Stone, but the messages show the two discussing what was being said about them in the media.

Stone has repeatedly denied he knew about the WikiLeaks October 2016 release before it happened.

“No, I had no advance notice of the source, content, or exact timing of the WikiLeaks disclosures regarding Hillary other than what had been stated by Assange in public—and there is no evidence to the contrary,” Stone said in an email to VICE News on Monday.

He’s also scheduled to appear Tuesday on MSNBC.

The timeline of Stone’s public statements about the hack have raised questions about what he knew and when.

Russian hackers first began trying to hack email accounts at the Democratic National Committee (DNC) and the Clinton campaign in the summer of 2015.

By March 19, 2016, hackers gained access to Clinton campaign chair John Podesta’s email account.

WikiLeaks published hacked DNC emails in July 2016, leading the committee’s chairwoman, Florida Rep. Debbie Wasserman Schultz, to resign amid protests about the DNC’s attempt to undermine the Bernie Sanders campaign, as revealed in the emails.

On Aug. 8, 2016, Stone said he had been in contact with Julian Assange and told a meeting of Republicans in Florida that more emails would be published soon: “I believe the next tranche of his documents pertain to the Clinton Foundation, but there's no telling what the October surprise may be.” He walked that claim back 10 days later, saying he'd been communicating with Assange through an intermediary.

On Aug. 21, 2016, Stone tweeted, “Trust me, it will soon be Podesta’s time in the barrel. #CrookedHillary.” Stone says he was referring to Podesta’s business dealings, not predicting the release of Podesta’s hacked emails.

On Oct. 2, 2016, Stone tweeted: “Wednesday @HillaryClinton is done. #Wikileaks.”

Five days later, on Oct. 7, 2016, WikiLeaks published Podesta’s hacked emails. The private Twitter messages obtained by The Atlantic show that Stone and WikiLeaks communicated on Oct. 13, 2016. The day after the election, WikiLeaks sent Stone a message saying, “Happy? We are now more free to communicate.” Stone did not respond.

The probe so far

Mueller has indicted 19 people and three companies so far in his investigation, which appears to have focused first on Russian efforts to spread divisive content through social media, with the end goal of supporting the campaigns of Donald Trump and Sen. Bernie Sanders.

Former Trump campaign manager Paul Manafort is charged with illegal foreign lobbying and money laundering, and former Trump campaign foreign policy adviser George Papadopoulos pleaded guilty for lying to the FBI about his efforts to connect Trump campaign advisers with Russian officials.

Unrelated to these charges, both Manafort and Papadopoulos reportedly discussed the Russian email hack with Russian-connected people before the hack was public knowledge.

In April 2016, two months before the hack was made public by the Washington Post, Manafort discussed the hack with a Russian-Ukrainian operative. Also in April 2016, Papadopoulos met a professor with connections to Russian government officials who told Papadopoulos that the Russians had “dirt” on Clinton in the form of “thousands of emails,” according to Papadopoulos’ plea deal. A memo prepared by Democrats on the House Intelligence Committee, declassified in February, alleges he also had prior knowledge of the plan to release the hacked emails, which didn’t happen until July 2016.

DNC hack timeline

Summer 2015: Russian hackers begin phishing operation on DNC.

November 2015: WikiLeaks writes to group of supporters, “We believe it would be much better for GOP to win.”

March 19, 2016: Russian hackers gain access to John Podesta’s email account.

April 2016: Russian hackers breach DNC again.

April 11, 2016: Manafort discussed the DNC hack, among other things, with Russian-Ukrainian operative Konstantin Kilimnik.

April 26, 2016: Trump campaign adviser George Papadopoulos met a professor with connections to Russian government officials who told him the Russians had “dirt” on Clinton in the form of “thousands of emails.” A Trump campaign supervisor congratulated Papadopoulos on making contact with the professor, saying “great work” in an email.

May 18, 2016: James Clapper says foreign spies are trying to hack Democrats’ digital networks.

June 3, 2016: British publicist Rob Goldstone emails Donald Trump Jr. about setting up meeting with Russian lawyer to discuss information that would “incriminate Hillary”: “This is obviously very high-level and sensitive information but is part of Russia and its government’s support for Mr. Trump.” Don Jr. responds: “Seems we have some time and if it’s what you say I love it especially later in the summer.”

June 14, 2016: Russian hack of DNC first reported by the Washington Post.

June 15, 2016: Trump blames DNC for hack: “We believe it was the DNC that did the ‘hacking’ as a way to distract from the many issues facing their deeply flawed candidate and failed party leader.”

July 22, 2016: WikiLeaks begins publishing DNC emails.

July 25, 2016: FBI announces investigation into DNC breach.

July 29, 2016: Democratic Congressional Campaign Committee says it’s been hacked too.

Aug. 8, 2016: Stone says he has communicated with Assange.

Aug. 18, 2016: Stone says on C-SPAN that he has been communicating with Assange through an intermediary.

Aug. 21, 2016: Roger Stone tweeted, “Trust me, it will soon be Podesta’s time in the barrel. #CrookedHillary.”

Sept. 26, 2016: Trump says he doesn’t think the hack was done by Russia: “I don’t think anybody knows it was Russia that broke into the DNC. [Clinton’s] saying Russia, Russia, Russia, but I don’t—maybe it was. I mean, it could be Russia, but it could also be China. It could also be lots of other people. It also could be somebody sitting on their bed that weighs 400 pounds, OK?”

Oct. 2, 2016: Stone tweets “Wednesday @HillaryClinton is done. #Wikileaks.”

Oct. 3, 2016: WikiLeaks wrote Don Jr. “Hiya, it’d be great if you guys could comment on/push this story,” including a quote from Clinton about wanting to “just drone” Assange. Don Jr. responds an hour and a half later: “Already did that earlier today.” “It’s amazing what she can get away with.”

Oct. 5, 2017: Stone tweets “Libs thinking Assange will stand down are wishful thinking. Payload coming #Lockthemup,”

Oct. 7, 2016: WikiLeaks published Podesta’s emails, one hour after NBS publishes the "Access Hollywood" tape. U.S. intelligence officials blame Russian government for hacks.

Oct. 12, 2016: WikiLeaks messages Don Jr. suggesting Trump tweet a link to WikiLeaks, adds “Btw we just released Podesta Emails Part 4.”

Oct. 14, 2016: Don Jr. tweets WikiLeaks link.

Nov. 6, 2016: WikiLeaks releases more DNC emails.

Nov. 8, 2016: Trump wins presidential election.