US election

Mr Obama praised Mrs Clinton at the Democratic convention in Philadelphia, as the most qualified person ever to run for the White House.

He said voters faced a choice between hope and fear, attacking "home-grown demagogue" Republican Donald Trump.

Mr Trump responded by rejecting the president's optimistic portrayal.

"Our country does not feel 'great already' to the millions of wonderful people living in poverty, violence and despair," he said on Twitter.

Mrs Clinton did not hand over 30,000 emails as part of an investigation into her private email server as they contained private details.

"Russia, if you're listening, I hope you're able to find the 30,000 emails that are missing," Mr Trump said on Wednesday.

"I think you'll be rewarded mightily by our press."

The emails would contain some "beauties", he said. Soon after, he wrote on Twitter that if anyone had the emails, they should hand them over to the FBI.

Debbie Wasserman Schultz's move follows a leak of emails appearing to suggest that party insiders tried to thwart the campaign by Hillary Clinton's rival.

Bernie Sanders had pressed for the party chairwoman to step down.

Mrs Clinton is to be officially nominated at the Philadelphia meeting.

The Vermont senator had said Ms Wasserman Schultz "should not be chair" of the Democratic National Committee.

"And I think these emails reiterate that reason why she should not be chair," he told ABC's This Week programme.

Endorsement

Her announcement would come ahead of the Democratic National Convention, which is due to begin on Monday in Philadelphia.

Senator Elizabeth Warren, a favourite choice among Democrats, has said she was "probably not" the choice.

Virginia Senator Tim Kaine has emerged as a leading contender for the role.

A vote that would allow delegates to back a candidate of their choice was quashed when three states reportedly backed out.

Some said the RNC sabotaged their efforts on purpose.

The push was the last gasp for those who hope to see a different Republican candidate get the nomination.

The nomination of Mr Trump has been a source of conflict in the party.