There is no actual federal crime of "collusion" in this kind of investigation, even though the word is popularly used to describe possible complicity between Trump associates and Russian operatives who tried to influence the 2016 presidential election.
Trump himself invoked the word "collusion" in a tweet on Tuesday related to the indictment of his former campaign chairman Paul Manafort, declaring that Manafort's lawyer said "there was 'no collusion' and events mentioned took place long before he came to the campaign."
In fact, Manafort and former Trump campaign official Rick Gates were charged with 12 counts tied to, among other offenses, unregistered lobbying with a foreign power and money laundering. They have pleaded not guilty. Many allegations date back years before the 2016 campaign, yet the two men are accused of laundering money through US and foreign corporations and bank accounts into 2016.
Separately, new public documents show that former Trump campaign adviser George Papadopoulos pleaded guilty to lying about his contacts with people connected to Russians who wanted to offer the Trump campaign "dirt" on 2016 Democratic nominee Hillary Clinton.
That 13-page plea statement is rife with references to emails and other communications tied to Russian contacts, evoking common conceptions of "collusion." Yet Mueller's team makes no such assertion in the plea statement or the 40-page transcript of Papadopoulos' October 5 arraignment and sentencing unsealed on Monday. The case further suggests the special counsel is watching for people who might try to cover their tracks by lying to investigators, with an eye toward using charges related to lying to leverage cooperation.
This all reflects standard prosecutorial practice, seeking the strongest case on specific offenses, with the evidence at hand -- and the goal of bigger targets who might be pulled in.
There were several signals Monday of more allegations to come, whether they be tied to a conspiracy, false statements or campaign finance law -- all possibilities beyond "collusion." Mueller demonstrated that he is willing to use the charge of lying as a tool in this investigation, and it is not known what people involved have so far told federal agents and the grand jury.
CNN's Katelyn Polantz contributed