Former Trump campaign chairman Paul Manafort agreed Friday to cooperate with the special counsel's Russia investigation as he pleaded guilty to federal charges and avoided a second trial that could have exposed him to even greater punishment.

The deal gives special counsel Robert Mueller a key cooperator who led the Trump election effort for a crucial stretch during the 2016 presidential campaign.

It is unclear what information Manafort is prepared to provide to investigators about President Donald Trump or that could aid Mueller's investigation into Russian interference in the 2016 presidential election. But the plea nonetheless makes Manafort the latest associate of Trump, a president known to place a premium on loyalty among subordinates, to admit guilt and cooperate with investigators in hopes of leniency.

AP Justice Department reporter Eric Tucker explains, "what's really significant about the cooperation is there is nothing that would stop Paul Manafort from describing to the special counsel acts and crimes and incidents that aren't what he pleaded guilty to."

"So if he has information that he is not admitting guilt to, he can still provide it to the government. He's still encouraged to provide it to the government. And that is information that of course could be about the campaign and could be about Donald Trump," Tucker adds.

The cooperation deal requires Manafort to provide whatever information the government asks of him, though it does not specify what if anything prosecutors hope to receive about Trump.

Given his direct involvement in the Trump campaign, including episodes being scrutinized by Mueller, Manafort could be positioned to provide key insight for investigators working to establish whether the campaign coordinated with Russia.

Manafort was among the participants, for instance, in a June 2016 Trump Tower meeting with Russians and the president's oldest son and son-in-law that was arranged so the campaign could receive derogatory information about Democrat Hillary Clinton. A grand jury used by Mueller has heard testimony about the meeting.

Friday's deal, to charges tied to Ukrainian political consulting work but unrelated to the campaign, was struck just days before Manafort was to have stood trial for a second time.

He was convicted last month of eight financial crimes in a separate trial in Virginia and faces seven to 10 years in prison in that case. The two conspiracy counts he pleaded guilty to on Friday carry up to five years in prison, though Manafort's sentence will ultimately depend on his cooperation.

In the past year, Mueller has secured pleas from a former national security adviser who lied to the FBI about discussing sanctions with a Russian ambassador, a campaign aide who broached the idea of a meeting with Russian President Vladimir Putin; and another aide who was indicted alongside Manafort but ultimately turned on him. The president's former personal lawyer has separately pleaded guilty in New York.

White House press secretary Sarah Sanders insisted that the Manafort case was unrelated to Trump.

"This had absolutely nothing to do with the president or his victorious 2016 presidential campaign. It is totally unrelated."

Washington DC - 5 June 2018

1. Paul Manafort walking toward US District courthouse

Alexandria, Virginia - 14 September 2018

2. SOUNDBITE (English) Eric Tucker, AP Justice Department Reporter:

"Today, former Trump campaign chairman Paul Manafort pleaded guilty to two federal counts. And most significantly, he agreed to cooperate and special counsel Robert Mueller's investigation. That is a very significant development because it means that he is going to be agreeing to testify and agreeing to provide any sort of information that the Special Counsel asks of him."

Alexandria, Virginia - 23 May 2017

3. Paul Manafort gets out of car and walks into US District courthouse

4. STILL photo of Manafort walking out of courthouse

Alexandria, Virginia - 6 November 2017

5. STILL photo of Manafort walking out of courthouse

Cleveland, Ohio - 17 July 2016

6. STILL photo of Paul Manafort talking to reporters at the Republican National Convention

Alexandria, Virginia - 14 September 2018

7. SOUNDBITE (English) Eric Tucker, AP Justice Department Reporter:

"He pleaded guilty to conspiracy against the United States. And in the course of that he admitted to all sorts of illegal conduct related to his Ukrainian political consulting work that he did over the course of many years. And the principal allegation, or one of the principal allegations, is that he worked as a foreign agent advocating in Ukraine for those political interests and did not register as such with the Justice Department. The Justice Department says if you're going to lobby in the United States on behalf of a foreign government, which is the allegation against Manafort, you have to register. But what's really significant about the cooperation is there is nothing that would stop Paul Manafort from describing to the special counsel acts and crimes and incidents that aren't what he pleaded guilty to. So if he has information that he is not admitting guilt to, he can still provide it to the government. He's still encouraged to provide it to the government. And that is information that of course could be about the campaign and could be about Donald Trump."

Cleveland, Ohio - 21 July 2016

8. Paul Manafort with President Donald Trump at the RNC rehearsal

ASSOCIATED PRESS - AP CLIENTS ONLY

Cleveland, Ohio - 17 July 2016

9. STILL photo of Paul Manafort talking to reporters at the Republican National Convention

ASSOCIATED PRESS - AP CLIENTS ONLY

Alexandria, Virginia - 14 September 2018

SOUNDBITE (English) Eric Tucker, AP Justice Department Reporter:

10. "So it's unclear exactly what information Manafort could have about Trump but it is important to note that Manafort led the Trump campaign during a very critical stretch of the 2016 campaign. He was a participant in a Trump Tower meeting in June 2016 that involved the president's son, his son in law Jared Kushner and Manafort and a Russian government lawyer. And the point of that meeting we know from Donald Trump junior himself was to accept and receive dirt about Hillary Clinton. And so that's a significant meeting. We know that Möller is interested in it. So to the extent that Manafort can provide information, I'm sure Mauler would be more than happy to hear anything that Manafort has to say about that."

ASSOCIATED PRESS - AP CLIENTS ONLY

New York - September 2014

9. Exterior shot of Trump Tower

ASSOCIATED PRESS - AP CLIENTS ONLY

Vancouver - 28 February 2017

10. FILE of Donald Trump, Jr. entering room with Eric Trump