WASHINGTON — A former top Trump campaign aide who became a star witness for Special Counsel Robert Mueller must serve 45 days in jail for his crimes despite his extensive assistance to prosecutors, a judge said.

Rick Gates’s testimony helped convict Trump confidant Roger Stone and send former Trump campaign manager Paul Manafort to prison. At Gates’s sentencing on Tuesday, the judge praised his work for the government but imposed a brief jail term for tax and lobbying crimes. Gates must serve his time intermittently during a three-year term of probation.

“I accept complete responsibility for my actions,” Gates told U.S. District Judge Amy Berman Jackson in Washington.

The sentencing ends one of the most explosive chapters of Mueller’s 22-month probe into Russia’s interference in the 2016 election and President Donald Trump’s possible obstruction of justice. Though Mueller didn’t tie Trump to a conspiracy with Russia, Gates helped establish that Manafort, his former boss, concealed millions of dollars paid to him by pro-Russia oligarchs for political consulting in Ukraine.

Gates is cited 63 times in Mueller’s 448-page report on Russian meddling and obstruction of justice.

The hearing included new details about Gates’s decision to cooperate at a sensitive time early in Mueller’s probe. According to prosecutor Molly Gaston, Manafort told Gates there would be what she called a “defense fund” for him if he chose not to aid the government.

Instead, she said, he “decided to do the right thing.”

Gates, Trump’s former deputy campaign chairman, will continue to work with prosecutors as part of his probation, though it’s unclear what that will entail. After the election, Gates served as deputy chairman of Trump’s inaugural committee, which has been investigated by federal prosecutors in New York.

Gates must also perform 300 hours of community service and pay a $20,000 penalty, the judge said.

Gates, 47, faced as long as five years behind bars. Prosecutors asked Jackson not to jail Gates, citing “extraordinary assistance” that included more than 50 meetings with federal and state investigators. Prosecutors and defense lawyers also asked that Gates not be fined, saying he’s suffered enough financially.

Manafort and Gates joined the Trump campaign in early 2016, but Manafort was forced to quit that August after media reports that he was improperly paid millions of dollars for his work in Ukraine. Gates continued working for the campaign and went on to serve on the inaugural committee.

The two were charged in October 2017 for crimes relating to their work before joining the campaign. Manafort, a longtime Washington lobbyist and Republican Party operative, had spent almost a decade working for the pro-Russian government of Ukrainian President Viktor Yanukovych and his Party of Regions. Yanukovych was driven from office and into exile in Russia by a 2014 revolution.

Mueller accused them of laundering tens of millions of dollars earned in the Ukraine and of concealing efforts to lobby the U.S. government on behalf of foreign clients. The charges were viewed as a form of leverage against the two as Mueller probed Russian interference in the election.

Gates later pleaded guilty to helping Manafort avoid millions of dollars in U.S. taxes and lobbying the U.S. illegally on behalf of Ukraine. He alsoadmitted failing to report his own income and confessed to stealing hundreds of thousands of dollars from Manafort to pay for an extramarital affair and other expenses.

At a monthlong trial featuring Gates as the star witness, Manafort was convicted in August 2018 of lying to tax authorities about tens of millions of dollars he earned as a political consultant in Ukraine and misleading banks about his financial health to get loans. He later pleaded guilty to conspiring to lobby illegally for Ukraine, to launder money to support a lavish lifestyle, and tamper with witnesses.

He’s serving a combined term of 7 1/2 years in a Pennsylvania prison and now faces additional charges in New York state.

Gates also testified at the trial of Roger Stone, who was found guilty last month of lying to Congress about his communications regarding WikiLeaks’ trove of stolen Democratic Party documents.

Gates told jurors he was riding in a limousine with Trump during the 2016 campaign when Stone called to tell the candidate that WikiLeaks, which had already released records damaging to rival Hillary Clinton’s campaign, would put out more documents. That account was included in Mueller’s report about Russian interference. Stone is due to be sentenced on Feb. 6.

Gates also appeared as a government witness in the failed prosecution of former Obama White House counsel Greg Craig, who was acquitted at trial on charges of illegal lobbying work for Ukraine.