For the first time a Russian is behind bars for having attempted to influence the US 2016 presidential campaign.

No longer accused. Guilty.

Does it implicate US President Donald Trump? Not directly, not yet. Not that we know of.

In the evidence brief provided by the FBI, Maria Butina was attempting to influence the Republican Party and other conservatives.

Not included in that brief is a direct encounter with Mr Trump.

The Washington Post reported that barely a month after Mr Trump declared his candidacy for the presidency, Ms Butina asked the candidate a question during a public forum about Russian sanctions and his plans towards Russia.

It was seemingly innocuous. Mr Trump issued his standard attack on President Barack Obama and added "I know Putin — I'll tell you what — we get along with Putin".

She also reportedly had a brief encounter with Don Junior, Mr Trump's son.

Prosecutors accused Butina of trying to infiltrate the powerful NRA gun lobby. ( Facebook )

But there is another more critical link to Mr Trump and his immediate family.

Butina's boyfriend, Republican activist Paul Erickson, was in contact with the Trump campaign.

He hasn't been charged yet, though he has reportedly received a "target letter" from investigators saying they may file conspiracy charges against him.

Mr Trump's argument that Special Counsel Robert Mueller's work is a "witch hunt" remains just an attempted smear.

Yes, Russians have been charged before — 13 Russians and three companies have been indicted with conspiracy to tamper with the 2016 election.

A further 12 Russian intelligence officers have been indicted for hacking Democratic Party targets.

But on Tuesday on US soil a Russian is prepared to plead guilty to being an illegal foreign agent, to working in the US at the direction of an unnamed "Russian official".

Maria Butina is expected to plead guilty to being a foreign agent after reaching a deal with prosecutors. ( AP: Jon Elswick. )

Title 18 of the US Code sections 371 and 951 make it clear from their titles:

371 Conspiracy

371 Conspiracy 951 Agents of Foreign Governments

The FBI literally has her communications in which she states "I am ready for further orders".

What this plea deal between Butina and the US Attorney's office does show is that the Mueller investigation is inching ever closer to the question of collusion.