In her June 2008 concession speech for the Democratic presidential nomination, Hillary Clinton pledged to do all she could to propel Barack Obama to the White House.
On Tuesday, he returns the favour.
After months of waiting on the sidelines while his former secretary of state battled Senator Bernie Sanders to be this year's Democratic nominee, the president hits the campaign trail in what is likely to be the first of many trips to urge voters to make his one-time rival his successor.
Obama endorsed Clinton last month with a forceful video in which he stated that no one had been so qualified for the job.
But a planned joint appearance shortly thereafter was postponed after the shooting at a gay night club in Orlando, Florida.
"I have seen her judgment, I've seen her toughness, I've seen her commitment to our values up close," the president said in the video.
"I'm with her. I am fired up, and I cannot wait to get out there and campaign for Hillary."
He starts in North Carolina, a state the president won in the 2008 general election but lost narrowly in 2012. Clinton wants to reclaim it for Democrats in 2016.
Obama's first campaign appearance with the former first lady will close a circle of sorts on a relationship that started cordially as colleagues in the US Senate, grew tense as rivals in the 2008 race, and became close as partners in the Obama administration when she served as his top diplomat.
"(He) has developed a deep appreciation for her toughness under fire and her commitment to a set of values that the president shares.... Those values are principally the reason the president believes that she is the best person to succeed him," White House spokesman Josh Earnest said on Friday.
Obama's focus on Clinton's strength of character is meant to shore up support among voters who find her untrustworthy, a weakness that presumptive Republican presidential nominee Donald Trump has sought to exploit.
Clinton also needs Obama to woo young and left-leaning voters who backed Sanders and made up part of the president's voting coalition in 2008 and 2012.
The president, meanwhile, needs a Clinton victory on November 8 to preserve his legacy on a range of issues including health care, climate change and immigration.
The North Carolina trip is reminiscent of a joint appearance Obama and Clinton made in Unity, New Hampshire, following their divisive primary fight in 2008.
Now Clinton is the candidate and the president, who leaves office in January, is her advocate.
