Obama shares stage with Hillary, makes powerful case for former rival

Just hours after FBI Director James Comey brutally slammed Hillary Clinton's State Department email practices, President Barack Obama appeared onstage with his former rival to back her as the next U.S President.

According to CNN, Obama appeared onstage with Clinton in Charlotte after lending her a ride from Washington on Air Force One and sought to confer his popularity on a candidate still struggling to gain voters' trust.

"I came away from that primary admiring her even more because during that year-and-a-half, I had a chance to see up close, just how smart she was and just how prepared she was, especially since I debated her a couple dozen times. I saw how even when things didn't go her way, she'd just stand up straighter and come back stronger," he said.

Without taking Trump's name, the President repeatedly slammed the billionaire by going after his "tough talk" and "phony bluster."

"I know the other guy talks about making America great again. America's really great. This is a choice between whether we are going to cling to some imaginary past or whether we're going to reach for the future."

When the crowd here began to boo at Obama's mention of Trump's policies, the President urged: "Don't boo. Vote!"

Clinton, too, reflected on her first failed campaign against Obama and thanked him for the support.

"I also know him as the friend that I was honored to stand with in the good times and the hard times. Someone who has never forgotten where he came from," she said.

Taking a jab at Trump and the conspiracy theories he has espoused about Obama's birthplace, Clinton said: "And Donald, if you are out there tweeting, it is Hawaii."

With polls suggesting that more Democrats trust Obama than Clinton, the President will no doubt be one of Clinton's most powerful surrogates in the general election.