President Donald Trump again attacked special counsel Robert Mueller's probe into Russia and the 2016 U.S. election on Tuesday, reiterating that his campaign did not collude with Moscow and saying collusion is not a crime anyway.

Trump commented hours before his former campaign chairman, Paul Manafort, went on trial on tax and bank fraud charges in Virginia. As the first trial in the 14-month Russia probe, the case throws a fresh spotlight on a federal criminal investigation that has dogged Trump's presidency.

Mueller is investigating whether Trump campaign officials worked with Moscow to try to sway the 2016 U.S. presidential election, something commonly referred to as collusion by the media and public officials.