This key Mueller witness is still cooperating — and he's likely an important figure in another Trump probe

Rick Gates, President Donald Trump's former deputy campaign chair, is still cooperating with federal investigators after playing a key role in Special Counsel Robert Mueller's investigation.

Mueller managed to flip Gates, who pleaded guilty to making false statements to the FBI and conspiracy against the United States. He, in turn, testified against his longtime associate Paul Manafort, who was the chair of Trump's campaign. Manafort eventually found guilty and then pleaded guilty for a slew of charges, including false statements, failing to register as a foreign agent, and various financial and tax crimes.

Gates also told Mueller about his and Manafort's interactions with Russian political operative Konstantin Kilimnik, who Gates thought was a spy, during the 2016 campaign, but the special counsel was unable to get to the bottom of this bizarre connection.

But even after Manafort has been sentenced and the Mueller report has been released, the government said Monday in a court filing that it would like to delay Gates' sentencing further as his cooperation continues.

There are at least two ongoing Mueller-related cases in which Gates's testimony might be relevant: the charges against Trump ally Roger Stone and Greg Craig, the former White House counsel for President Barack Obama. Mueller also indicated in his report that there were a dozen additional cases about that have been spun off from the Russia investigation to other offices in the Justice Department, and Gates' testimony might be relevant in any number of them.

One particularly intriguing possibility is the ongoing investigation in the Southern District of New York and elsewhere of Trump's inauguration. Gates was the deputy chairman of the inaugural committee, so if there was any criminal wrongdoing surrounding the event, he may have information about it.