Hillary Clinton's campaign team have questioned the timing of the Federal Bureau of Investigation's probe into her personal email use.
FBI head, James Comey, is under pressure to reveal what the bureau knows and explain what Mrs Clinton has allegedly done wrong.
Donald Trump has welcomed the latest revelations in the email scandal that has embroiled his presidential rival Hillary Clinton.
The Republican hopeful called the new development, which has seen the FBI reopen its investigation into emails Clinton sent over a private server, part of "the biggest political scandal since Watergate", the 1970s scandal that forced the resignation of President Richard Nixon.
Trump has repeatedly attacked FBI Director James Comey for not indicting Clinton for her handling of classified information while US secretary of state from 2009 to 2013, but the new developments have prompted him to change his tune.
"As you know, I've had plenty of words about the FBI lately, but I give them great credit for having the courage to right this horrible wrong. Justice will prevail," he told a crowd in Cedar Rapids, Iowa.
The emails were found on a laptop seized from Clinton's aide's estranged husband, ex-congressman Anthony Weiner.
The FBI Director's letter has placed a dark cloud of suspicion over Mrs Clinton, and no one - perhaps not even he himself - knows why.
The presidential candidate has called for the FBI to fully explain the new emails that have come to light.