A day before the opening of President Donald Trump's Senate impeachment trial, former Vice President Joe Biden's campaign is issuing a pre-emptive strike, sending an unusual open memo to the media warning against disinformation pushed by the president and his defenders. The memo, first obtained by NBC News, is also a shot across the bow of Republican senators as they consider whether to entertain Trump's demands to call Hunter Biden, Joe Biden's son, as a witness in the trial. Trump has been "spreading a malicious and conclusively debunked conspiracy theory" that "Biden engaged in wrongdoing when he executed official United...