President Donald Trump has brushed off the first indictments in the probe of his campaign's ties to Russian election meddling, but the charges send a clear signal to the White House and other Trump associates: Robert Mueller means business.
By going after Mr Trump's campaign manager and another aide on money-laundering charges and securing a guilty plea from a third campaign adviser, the special prosecutor showed he would delve deeply into the past in search of criminal activity and use his broad powers aggressively.
That's left some Mr Trump associates worried about what or whom Mueller will target next, despite the White House's public dismissal of the developments as unrelated to the president and his campaign.
"They're flexing their muscles for anybody that they approach in this investigation and letting them know we really mean it," said former federal prosecutor Patrick Cotter. "So if we come to you, you should talk to us. Manafort didn't and look what happened to him."
Mr Manafort and Rick Gates are charged with money laundering, tax fraud, conspiracy to defraud the United States, and other counts. They pleaded not guilty on Monday.
The indictments, which closely detail the alleged crimes, appeared to be an opening salvo from Mr Mueller.
Mr Trump has denied any collusion with Russia and at times described the investigation as a "hoax" and a "witch hunt." Russia has denied interfering with the 2016 election.
With the first indictments on Monday, Mr Mueller showed he was not afraid to use his powers, and Trump officials noticed.
"One thing I'm worried about in a bigger scale is that Rosenstein, by giving Mr Mueller this wide berth, has created this monster," said one former White House official, who spoke on condition of anonymity.
A former Trump campaign adviser fretted that the probe could, as a result, touch on Mr Trump's businesses, too.
In a New York Times interview in July, Mr Trump indicated that Mr Mueller would be crossing a red line if he investigated Mr Trump's family business.
A number of lawyers said the guilty plea of George Papadopoulos, announced by Mr Mueller's team on Monday, could ultimately provide a closer link to the campaign and pressure others to open up.
While the charges against Mr Manafort and Mr Gates were not related to their campaign work, Mr Papadopoulos admitted he lied to the Federal Bureau of Investigation about his contacts with foreign nationals he believed to be tied to the Russian government while he was a campaign adviser.
"God knows what this guy's going to say now," said the former Trump campaign adviser.