On Friday, Gates pleaded guilty to two additional charges on the same day they were issued: conspiracy against the U.S. and lying to federal investigators. He still faces a prison sentence of nearly six years, but the special counsel has the ability to request a shorter sentence for him.
That tool could be crucial for Mueller's team, who could use the leverage of a lighter prison sentence to yield more valuable information from Gates about the ongoing Russia probe.
Gates was deeply involved in the inner workings of the campaign, and remained a part of Trump's election bid even after Manafort resigned in August 2016. Gates also worked as a liaison between the campaign and the Republican National Committee, and was involved in the presidential transition after the election.
Manafort, on the other hand, has maintained his innocence even as he continues to rack up charges.
"I had hoped and expected my business colleague would have had the strength to continue the battle to prove our innocence. For reasons yet to surface he chose to do otherwise," Manafort said following Gates' change of plea.
The former campaign chairman, 68, was hit with five additional criminal counts on Friday, including lying, conspiracy to launder money and acting as an unregistered foreign agent.