White House counsel Don McGahn, whose relationship with United States President Donald Trump has been strained by the investigation into Russian interference in the 2016 presidential election, is to leave his job. Mr Trump announced on Twitter on Wednesday that Mr McGahn would leave after the US Senate confirms the nomination of Brett Kavanaugh to the Supreme Court. He will become the latest in a long line of high-ranking advisers to leave the president’s side. Mr McGahn did not know the tweet was coming, an administration official said, but he had planned to leave the White House because he felt he had achieved his goals in getting conservatives named to federal judgeships, in rolling back regulations and in reeling in bureaucracy. <strong>_______________</strong> <strong>Read more:</strong> ><strong>_______________</strong> Mr Trump announced Mr McGahn’s departure less than two weeks after it was reported that the aide had voluntarily co-operated with special counsel Robert Mueller’s investigation of Russian meddling and possible collusion with the Trump campaign, which the president repeatedly has decried as a "witch hunt". In his interviews with Mr Mueller's team, Mr McGahn was asked about Mr Trump's actions in firing FBI director James Comey in 2017, the <em>Washington Post</em> reported. Other topics included Mr Trump's criticism of attorney general Jeff Sessions and his deputy Rod Rosenstein, who oversees the Russia probe, the <em>Post</em> said. Mr Trump later told reporters at the White House that he had “a lot of affection for Don” and said he was not concerned about what Mr McGahn told the Mueller probe. “We do everything straight,” he said. “We do everything by the book. And Don is an excellent guy.” Mr Mueller’s investigation has led to guilty pleas from Trump insiders, indictments, co-operation deals and one conviction. Russia has denied meddling in the election. The president has not settled on a replacement for McGahn, White House spokeswoman Sarah Sanders said. There has been speculation the job would go to Emmett Flood, a veteran Washington lawyer who joined the White House in May to help with the Russia probe. “People like him,” Ms Sanders said of Mr Flood. “He’s super well-respected around the building but there’s not a plan locked in place at this point.” Mr McGahn could not be reached for comment. With his departure, he is part of an unprecedented level of turnover among modern US governments. Of Mr Trump's top 27 aides listed on his first annual staff report to Congress, Mr McGahn will be the 17th to depart. The news was met with dismay by Senate Judiciary Committee Chairman Chuck Grassley, who wrote in a tweet addressed to Trump: “U can’t let that happen.” George Hartmann, spokesman for the committee, said Mr Grassley viewed Mr McGahn as the linchpin to the president’s push to fill judicial vacancies. Senate Republican leader Mitch McConnell praised Mr McGahn as “the most impressive White House Counsel during my time in Washington”. With help from Mr McGahn, Mr Trump has reshaped the federal judiciary in a conservative direction, tilting the balance on the Supreme Court to the right, and filling a record-breaking number of seats on the influential federal appeals courts during his first two years in office. Mr Trump’s success in filling vacancies has been key to building and retaining political support among Republican voters. Mr McGahn had threatened to quit in June 2017 because he was “fed up”, after Mr Trump insisted he took steps to remove Mr Mueller, a source told Reuters earlier this year. Mr McGahn was involved in the controversy surrounding Mr Trump’s firing of former national security adviser Michael Flynn. In January 2017, then-acting attorney general Sally Yates informed Mr McGahn that Mr Flynn had misled the FBI about his discussions with former Russian ambassador to the US, Sergei Kislyak. Mr Flynn pleaded guilty in December 2017 to lying to the FBI. Mr McGahn, a Washington insider who was chief counsel for Trump’s presidential run, was one of the first advisers Mr Trump appointed to the White House after the November 2016 election.