WASHINGTON (Reuters) - Special counsel Robert Mueller asked the White House to save all documents related to a meeting last year between Donald Trump Jr and a Russian lawyer he was told had damaging information on his father’s presidential rival, Democrat Hillary Clinton, CNN reported on Friday.  Mueller, who leads the criminal probe into possible collusion between the Trump campaign and Russia to sway the November presidential election, told White House counsel Don McGahn in a letter that the June 2016 meeting was relevant to his investigation, CNN reported. It cited a copy of the letter. 