(CNN)Special counsel Robert Mueller has subpoenaed the Trump Organization for business documents -- some of which are related to Russia, according to The New York Times -- a move that represents the latest evidence that the probe seems to have widened to include far more than simply Russia's attempts to meddle in the 2016 presidential election.
The details of the subpoena are not available. That fact makes it hard to know exactly what Mueller is looking for, what it has to do with Russia or the Trump Organization's business in the country and why he needed to subpoena the documents as opposed to simply asking for them.
But what we do know is that President Donald Trump -- and his lawyers -- have warned Mueller against a widening of the probe to include things that happened before Trump became a candidate or having to do with his real estate business.
In an interview with The New York Times in July 2017, Trump was asked whether Mueller looking into his personal finances -- not involving Russia -- would amount to a "red line"-like violation in his mind. Here's how he responded:
"I would say yeah, I would say yes. By the way, I would say, I don't -- I don't -- I mean, it's possible there's a condo or something, so, you know, I sell a lot of condo units, and somebody from Russia buys a condo, who knows? I don't make money from Russia."
Because of the lack of specificity regarding the subpoenas, we have no way of knowing if Mueller's latest request directly violates that red line. But whether or not it violates the letter of Trump's red line matters less than whether Trump feels as though Mueller's latest inquiry is a step too far.
Trump has been very clear about his feeling on the Mueller investigation, which he has described as a "witch hunt" and a "hoax." He has also been very, very clear that there has been no collusion between his campaign and the Russians. And that the Justice Department should spend its time looking into allegations against Hillary Clinton rather than wasting time on the Russia investigation.
Asked about the Times report on Thursday afternoon, White House press secretary Sarah Sanders said only "there was no collusion between the Trump campaign Russia." She repeated that same line when asked a similar question about the red line later in the briefing.
Trump attorney Ty Cobb declined a request for comment.
Trump's Twitter feed lay dormant in the immediate aftermath of the Times report on Mueller's latest subpoena. But the context of this week suggests Trump may well be in a firing mood. He parted ways with Secretary of State Rex Tillerson -- via Twitter(!) -- earlier in the week and made clear more changes would be on the way.
"We're getting very close to having the Cabinet and the other things that I want," Trump said shortly after firing Tillerson.
Sources suggest that national security adviser H.R. McMaster, Veterans Affairs Secretary David Shulkin and Housing and Urban Development Secretary Ben Carson are all on thin ice, with some reports detailing specific replacements being considered for each of them. And Trump has made little secret of his displeasure with Attorney General Jeff Sessions -- specifically Sessions' decision to recuse himself from the Russia investigation.
On Thursday, Trump pushed back on reports that a staff shakeup was imminent, calling it "exaggerated" and "fake news."
Will Trump take umbrage at Mueller's latest move and use it as an excuse to fire Sessions? Will he go even further, risking political suicide by firing Mueller? Or will he stay cool?
Predicting what Trump does on any subject is next to impossible. Predicting what he will do on the Russia investigation -- which has long been an issue on which Trump reacts more on an emotional level than an intellectual one -- is plain impossible.
