'Russian collusion’: Mueller witnesses reveal what they think the special counsel is focused on

Special Counsel Robert Mueller's Russia investigation has received an incalculable amount of media coverage, but in many ways, it still remains opaque to the country. In large part, this is because the special counsel's team has been unusually leak-proof, and Mueller himself has deliberately spoken zero words to the press about his work.

But this week, MSNBC"s Ari Melber hosted on "The Beat" four of the witnesses that Mueller has spoken to — and they gave unique insight into the inner workings of the investigation. While some of the discussion devolved into bickering, some of it was, in fact, intriguing. Like everyone involved in the investigation, they all have their own biases and interests, so their pronouncements cannot be taken entirely at face value. They nevertheless provide a rare window into the probe.

Michael Caputo, a Trump campaign staffer who has previously lived in Russia, confirmed that, despite what some had once thought, the "collusion" element of Mueller's investigation remained a focus last year.

"In May of 2018, they still believed in Russian collusion," he said. "It was very obvious to me. A lot of the questions they asked me showed it very clearly."

He added: "I believe right now that they still think there was some form of coordination."

It's noteworthy that, at this time — May 2018 — Mueller was already known to have the active cooperation and guilty pleas of two witnesses with shady ties to Russia: Michael Flynn and Rick Gates.

Melber pushed Caputo to explain whether the focus was just on the campaign colluding with Russia, or if it included the president's potential collusion as well.

Caputo said he didn't think the Mueller team thought Trump was involved, but Sam Nunberg, another witness who joined and left the campaign in 2015, disagreed.

"They asked me immediately how often Trump talked to Stone," Nunberg said. He confirmed that this suggests to him that they're probing the theory that Roger Stone, a long-time Trump ally who at one time claimed to be in contact with WikiLeaks founder Julian Assange, was a "linchpin" in coordinating between Trump himself and Russia.

Nunberg said he thinks the special counsel has a "highly circumstantial case" of election-related conspiracy — unless there some evidence he hasn't seen that "shocks the conscience."

"What they're really going to go for is pay-for-play," predicted Nunberg. "They've asked me about so many business interests — including Kushner's."

"Corruption?" asked Melber. "Of people around the president, or including the president?"

"Corruption," Nunberg confirmed, particularly during the transition period. "Including the president," he added.

None of this is well outside the bounds of what has been reported — though Nunberg's note that Trump's son-in-law Jared Kushner appears to be of keen interest to Mueller is especially noteworthy. But all of it is valuable for outsider observers because it comes from on-the-record sources who are known to have had direct contact with Mueller's team.

One topic that neither Caputo nor Nunberg mentioned was obstruction of justice, a charge that is almost certainly under consideration and investigation by Mueller, according to multiple public accounts. But since most of the obstruction of justice that observers believe Mueller might be interested would have happened during Trump's time in the White House, it's not surprising that witnesses who were only involved in the campaign would have little insight into the topic. Most of the people who would know about this topic have worked in the White House and thus have strong ties to Republican Party politics — giving them good reasons not to reveal what they may know about the ongoing investigation.