Trump’s outburst “could just be another rant,” said Elie Honig, a former federal prosecutor in the Southern District of New York who handled organized-crime cases. But on the other hand, it could signal action on the part of prosecutors that Trump registers as a threat. Honig explained that prosecutors sometimes get fed up with people they know are not being honest and threaten to bring charges against them. They may also threaten a person’s status as a potential cooperator, which typically comes with reduced charges. “My hunch is that prosecutors had some sort of ‘Time to get real’ conversation with someone implicated in the investigation, which was then relayed to Trump by defense attorneys,” Honig said.

The collective hunch in Washington that Mueller is due for his next big move could also be adding to Trump’s anxiety. The special counsel’s last major indictment came in July, when he brought charges against 12 Russian intelligence officers for hacking emails from the Democratic National Committee and a top Hillary Clinton campaign official in 2016. The four-month delay since the last indictment, combined with Mueller’s intensified interest in the Trump campaign’s relationship with WikiLeaks and Roger Stone, has left some observers with the sense that the investigation, tightly bottled up before the midterms, is ready to explode.

Like Honig, the former federal prosecutor Dan Goldman suggested that if Trump has learned anything about Mueller’s recent moves, it’d likely be from defense lawyers whose clients have been ensnared in the investigation. Goldman, who worked on mob-related cases in the Southern District of New York, speculated that the president may know in advance that “indictments are coming, probably tomorrow.” The special counsel’s office has a pattern of releasing indictments on Fridays.

Read: Trump repeatedly threatens retaliation against Russian investigators

The recent rumors about forthcoming indictments have not been baseless. Donald Trump Jr. has reportedly been telling friends that he expects to be indicted as early as this month, though it’s still unknown what he would be charged with. Roger Stone has also said he is “prepared” to be indicted “for some extraneous crime pertaining to my business, or maybe not even pertaining to the 2016 election.” (Stone’s shifting story to the House Intelligence Committee about his interactions with WikiLeaks in 2016 may have left him exposed legally.)

And a Stone associate, the right-wing conspiracy theorist Jerome Corsi, said earlier this week on a live-streamed video that he’d been informed by the special counsel that he will be indicted for lying to investigators. Prosecutors apparently confronted him with phone and email records that contradicted his testimony. After repeated interrogations, “my mind was mush,” he told NBC News.