WASHINGTON (Reuters) - Former FBI Director Robert Mueller has been cleared by U.S. Department of Justice ethics experts to oversee an  investigation into possible collusion between then-candidate Donald Trump’s 2016 election campaign and Russia, a spokeswoman said on Tuesday.  The department appointed Mueller special counsel last week to ensure an independent probe, but an ethics rule limiting government attorneys from investigating people their former law firm represented raised questions over how Mueller would be allowed to operate. Mueller’s former law firm, WilmerHale, represents President Trump’s son-in-law Jared Kushner, who met with a Russian bank executive in December, and the president’s former campaign manager Paul Manafort, who is a subject of a federal investigation. Kushner is now a White House adviser. Manafort quit the campaign last August, months before the Nov. 8 election. “Under the Rules of Professional Responsibility, Mr. Mueller is permitted to participate in matters involving his former firm’s clients so long as he has no confidential information about the client and did not participate in the representation,” Justice Department spokeswoman Sarah Isgur Flores said in a statement. Although Mueller has now been cleared by the Justice Department, the White House may still use his former law firm’s connection to Manafort and Kushner to undermine the findings of his investigation, according to two sources close to the White House. 