After months on the sidelines, President Barack Obama joined Democratic presidential candidate Hillary Clinton on the campaign trail at a rally in North Carolina on Tuesday, telling voters he was ready to "pass the baton" to his former secretary of state.

Obama took the microphone in Charlotte, chanting "Hillary!" and told the crowd there had never been a candidate as prepared to be president as Clinton, his rival in 2008 for the Democratic nomination.

"I've run my last campaign, and I couldn't be prouder of the things we've done together, but I'm ready to pass the baton," Obama said, in what was likely to be the first of many trips this year on Clinton's behalf.

"I know Hillary Clinton is going to take it, and I know she can run that race," he said.

Obama was returning the favor after Clinton backed him in 2008's general election. This year, he waited while she battled U.S. Senator Bernie Sanders for the Democratic nomination before endorsing Clinton last month once she became the party's presumptive nominee.

In Charlotte, Clinton preceded Obama, saying, "We're going to build on the vision for America that President Obama has always championed, a vision for a future where we do great things together."

The North Carolina trip came the same day that Federal Bureau of Investigation Director James Comey said the agency would not recommend that Clinton face criminal charges over her use of a personal email system while secretary of state.

White House spokesman Josh Earnest said Obama did not get advance notice of Comey's announcement and said the president would not discuss the FBI's investigation with Clinton.

Clinton's campaign welcomed the end of a probe that had cast a cloud over her campaign, but Republicans seized on Comey's criticism of what he termed Clinton's "extremely careless" handling of emails.

Presumptive Republican nominee Donald Trump, who was due to campaign in Raleigh, North Carolina, on Tuesday, criticized FBI recommendation, tweeting, "As usual, bad judgment."

Joint Appearance Delayed

The first joint campaign appearance by Obama and Clinton was initially planned for soon after she clinched the Democratic nomination. But it was postponed following the mass shooting on June 12 at a nightclub in Orlando, Florida.

On Tuesday, Obama appeared at ease back on the campaign trail. He mocked Trump's promise to "Make America Great Again," saying, "America is really great."

And he sought to contrast Clinton's preparedness for the White House and passion for helping working families with Trump, a political neophyte he referred to at times as "the other guy."

"Everybody can tweet, but nobody actually knows what it takes to do the job until you've sat behind the desk," he said, an apparent reference to the wealthy New York businessman's fondness for Twitter.

Clinton hopes to reclaim North Carolina for the Democrats in the Nov. 8 election. Obama won the state in the 2008 general election but lost it narrowly in his 2012 re-election.

Obama's appearance with the former first lady closes a circle on a relationship that began cordially when the two were U.S. Senate colleagues, grew tense when they were presidential rivals in 2008, and became close when Clinton served in Obama's Cabinet during his first term.

Clinton and her family have played a role in Obama's elections. Clinton and Obama appeared together in Unity, New Hampshire, following their divisive primary fight in 2008, and Clinton's husband, former President Bill Clinton, gave a well-received speech at the 2012 Democratic convention.

Obama has focused on what he touts as Clinton's strength of character, in hopes of shoring up support among voters who find her untrustworthy, a weakness Trump has sought to exploit.

Clinton needs Obama to woo young and left-leaning voters who backed Sanders and who made up part of the president's voting coalition in 2008 and 2012. Clinton has also campaigned with high-profile liberal U.S. Senator Elizabeth Warren, and she will appear later this week with Vice President Joe Biden.

Clinton and Obama traveled to North Carolina on the presidential plane Air Force One, which Trump characterized as a burden on taxpayers. A Clinton spokesman said the campaign would cover its portion of the travel costs.

(With inputs from agencies)