Rick Gates, a former top official in President Trump's campaign, leaves the federal courthouse in 2018. (Evelyn Hockstein/For The Washington Post)

On Wednesday, a federal judge ruled that President Trump’s former campaign manager Paul Manafort had violated his plea agreement by repeatedly lying to federal investigators. When Manafort first agreed to cooperate with special counsel Robert S. Mueller III’s office, it appeared he could be the key to helping Mueller determine whether there was a conspiracy between Russians seeking to influence the election and members of the Trump campaign. Now that Manafort has blown his plea agreement and seems to be heading to prison, attention is likely to shift to someone else cooperating with Mueller: Rick Gates, Manafort’s close associate and Trump’s former assistant campaign manager.

Manafort came to the Trump campaign with extensive personal and business ties to Russia. He was campaign manager during the critical summer of 2016, when Democratic emails stolen by the Russians were beginning to be leaked and when the Republican Party platform was changed to be more favorable toward Russia. He attended the June 2016 meeting at Trump Tower between senior Trump campaign officials and Russians promising “dirt” on Hillary Clinton. Manafort clearly was in a position to provide Mueller’s investigators with relevant information, whether good or bad for the president. He had a chance to reduce the lengthy prison sentence he is facing. All he had to do was tell the truth.

But Manafort chose to lie. In particular, the judge found he lied about his dealings, both during and after the campaign, with Konstantin Kilimnik, a longtime Manafort associate with suspected links to Russian intelligence. In court filings, prosecutors said they believe Manafort may have feared that if he told the truth it would jeopardize his chances for a presidential pardon. It’s also possible Manafort is simply afraid to cooperate, given that the Russian intelligence service has been known to poison those who cross them. But for whatever reason, Manafort decided he would rather risk life in prison than tell prosecutors the truth about his interactions with a suspected Russian spy while he served as the head of Trump’s campaign.

Enter Gates, Manafort’s longtime business associate and right-hand man. Gates and Manafort were indicted together in the Eastern District of Virginia for financial crimes related to their years of work in Ukraine. Gates pleaded guilty in that case and testified as a key government witness against Manafort, who was found guilty on eight felony counts. In the six months since that verdict, Gates has slipped from public view but has continued to cooperate with federal prosecutors.

Gates, like Manafort, was in a position to know a great deal of critical information. For example, recent attention has focused on an August 2016 meeting at a cigar club in New York where Manafort may have passed confidential campaign polling data to Kilimnik. Prosecutors have characterized that meeting as going “very much to the heart of what the special counsel’s office is investigating.” Gates was the only other person at that meeting. Indeed, it’s likely Gates’s cooperation helped prosecutors prove Manafort was lying to them about what happened there.

Recently we also learned that prosecutors in the Southern District of New York issued a grand jury subpoena seeking information related to possible financial improprieties or illegal foreign contributions to the president’s inaugural committee. The committee was chaired by Trump’s longtime friend, real estate developer Thomas J.Barrack Jr. Barrack’s deputy chairman? None other than Rick Gates. If there was wrongdoing connected to the inaugural committee, Gates likely knows. In fact, he already admitted at Manafort’s trial that he may have personally misused inaugural funds.

Others who have cooperated with Mueller, such as former national security adviser Michael Flynn and Trump’s former personal attorney, Michael Cohen, have moved forward to sentencing, which suggests their cooperation is largely completed. Gates, on the other hand, has had his sentencing date put off several times, most recently in January, when prosecutors said he continues to cooperate in “several ongoing investigations.” Prosecutors clearly are pleased with the extent and truthfulness of Gates’s cooperation; Manafort has shown us what happens to a cooperator who tries to pull the wool over Mueller’s eyes.

We don’t know whether Mueller will ultimately bring criminal charges involving a conspiracy between Russians and members of the Trump campaign. We don’t know what the investigation of the inaugural committee or other cases being pursued outside of Mueller’s shop will find. Rick Gates has stayed out of the limelight, but it’s becoming increasingly clear that he will play a crucial role in helping prosecutors find the answers.