NEW YORK/WASHINGTON - Lawyer Emmet Flood, who advised President Bill Clinton in impeachment proceedings, will assist President Donald Trump with Special Counsel Robert Mueller's investigation into Russia's role in the 2016 election, replacing Ty Cobb, White House spokeswoman Sarah Sanders said on Wednesday.The latest lawyer shuffle comes as the question of whether Trump will agree to an interview with Mueller appears to be coming to a head. Washington lawyer John Dowd, who left Trump's outside legal team over a month ago, said on Tuesday that in March Mueller had threatened to subpoena Trump's testimony if he did not talk to investigators.Flood will "represent the president and the administration against the Russia witch hunt," Sanders said. "Ty Cobb, a friend of the president, who has done a terrific job, will be retiring at the end of the month."Neither Cobb nor Flood immediately responded to requests for comment.Mueller is investigating Russia's meddling in the 2016 U.S. election, an investigation that includes whether the Trump campaign colluded with Moscow and possible obstruction of justice by Trump, among other things.Russia has denied interfering in the election, despite the conclusions of U.S. intelligence agencies, and Trump has denied there was any collusion between his campaign and Moscow while repeatedly denouncing the investigation.Last year, Flood turned down a post on the White House team that ultimately went to Cobb, Reuters reported in July. He met with Trump in March about assisting the administration with the Russia probe, though the position was unclear, a person familiar with the matter told Reuters at the time.Flood advised Clinton in impeachment proceedings in the late 1990s brought by the U.S. House of Representatives and tried before the U.S. Senate, where Clinton was acquitted.Flood also spent two years in the White House counsel's office, where he handled executive privilege-related disputes for President George W. Bush's administration and congressional investigations and other inquiries. He was a clerk for Associate Supreme Court Justice Antonin Scalia.Cobb joined the administration in July after resigning from the Washington law firm of Hogan Lovells. In an interview with Reuters in August he predicted a quick end to the Mueller probe."I'd be embarrassed if this is still haunting the White House by Thanksgiving, and worse if it's still haunting him by year end," Cobb told Reuters at the time.Trump has since appeared increasingly frustrated with the investigation. Last month, he brought former New York City Mayor Rudy Giuliani onto his outside legal team, saying the former federal prosecutor wanted to resolve the matter quickly.Former federal prosecutors Martin Raskin and Jane Serene Raskin also just joined Trump's outside legal team, which has recently been led by lawyer Jay Sekulow.