Senator Bernie Sanders has called on his supporters to back Hillary Clinton in the Presidential race telling supporters who were cheering him on, "This is the real world that we live in."

Sanders speaking in Philadelphia called Trump "a bully and a demagogue." He said Trump has made "bigotry and hatred the cornerstone of his campaign." and called him a "danger" for the future of the United States, that "must be defeated."

He also drew cheers when he noted that DNC chairwoman Debbie Wasserman Schultz resigned from her post.

Emails among DNC employees were released by anti-secrecy group WikiLeaks over the weekend appearing to expose favoritism for Clinton over Sanders.

The Federal Bureau of Investigation is investigating the nature and scope of a cyber intrusion at the Democratic National Committee, the agency said, amid concerns hackers working for Russia are attempting to use the breach to influence the U.S. presidential election.

Clinton campaign manager Robby Mook told CNN that the emails were released by suspected Russian hackers in order to sow discord at the convention and help Republican nominee Donald Trump, her rival in the Nov. 8 presidential election.

The Trump campaign dismissed the allegation as absurd.