First Lady Michelle Obama flew to North Carolina Thursday to join her new political partner Hillary Clinton on the stump, declaring her someone steady who can be trusted with the nuclear codes.

Obama, who brought star power to the Winston-Salem, N.C., rally, called Clinton, a onetime political rival of her husband, a friend and praised her determination. Clinton, in turn, asked the crowd, “Seriously, is there anyone more inspiring than Michelle Obama?”

She added, “As Michelle reminds us, this election is about our kids, and in my case, our grandkids. We have a job to do. Starting right now, let’s come together. Let’s work together and be hopeful and optimistic and unified.”

Obama told the audience that America needed a president “who takes this job seriously, and who has the temperament and maturity to do it well.  Someone who is steady, someone who we can trust with the nuclear codes, because we want to go to bed at night knowing that our kids and our country are safe.”

With Obama aiming to secure her husband's legacy and Clinton needing to drive women to the polls, the two women sought to celebrate their new political marriage of mutual interest, and reassure voters it's real.

Since she's emerged as Clinton's headline-grabbing surrogate, people wonder one thing, Obama noted.

"Yes, Hillary Clinton is my friend," she answered.

It's a reasonable question, given the two women's contrasting pasts and the nearly opposite way they've occupied the East Wing.

Clinton dived into policy, undertook a massive project and failed under a harsh spotlight. Obama largely steered clear and enjoyed quieter, more modest success. Both Ivy League-trained lawyers with their own careers, Clinton bridled under the stereotypes associated with the office, while Obama declared herself "mom-in-chief." While Clinton first held onto her maiden name, her Democratic successor let it known she prefers the "Mrs." title before her last name.

And when her time in the White House was ending, Clinton began planning her return to Washington.

Obama hasn't hidden her readiness to leave. The White House has quickly and repeatedly shot down any talk of the first lady continuing in politics after her husband leaves office.

Even as she explained her passion for Clinton's bid on Thursday, Obama acknowledged she is a reluctant politician.

"I would not be here," she said Thursday, if she didn't believe Clinton would be a president she would trust.

"I believe with all of my heart that Hillary Clinton will be that president," she said.

Democrats have relished Obama's speeches in support of Clinton as high points of the campaign cycle.

Obama's passionate response to Donald Trump's vulgar comments about women brought an emotional resonance to Clinton's bid that the candidate, who rarely gets personal on the stump, doesn't often deliver.

Obama's appearances have become a key part of Clinton's effort to fire up women -- particularly black women, for whom she's a model and a source of pride. Both Clinton and Obama on Thursday revived a line from her DNC speech -- "When they go low, we go high" -- turning it into a call and response.

The North Carolina event drew some 11,000 people, according to the fire marshal, one of largest crowds of Clinton's campaign. The audience roared as the two women walked onstage, turned to each other and embraced.

The new partnership has on one level made for a striking political odd couple.

As first lady, Obama has largely dodged controversial issues. She's stayed focused on her projects involving healthy eating, exercise, support for military families and education for girls -- and not publicly expressed opinions on thornier subjects. She's mastered the art of advocacy through popular culture, while, in recent years, all but ignoring the possibility of policymaking through legislation. She's cultivated a brand built on style, glamor and fashion.

It's a tenure that bears little resemblance to her Democratic predecessor in the East Wing. Clinton came in promising, along with her husband, a new kind of partnership in charge at the White House.

Hillary Clinton was a veteran of the feminist movement and ready to expand the office of first lady to suit her experience and passion for policy. She had an office in the West Wing, took over the health care overhaul effort and ultimately became a target of investigations and criticism alongside her husband.

It was a history Obama and her aides sought to avoid. Asked to cite role models, Obama has named Eleanor Roosevelt and Jacqueline Kennedy. The Clintons and Obamas, of course, have a fraught history, one that includes both spouses.

While Barack Obama and Hillary Clinton battled in 2008, Michelle Obama raised questions about her husband's opponent, framing the choice between the two as "about character."

Since then the women have publicly buried the hatchet. They've appeared at countless events together and heaped praised on each other's work, although there's little sign they've spent time one-on-one.

Comparing how first ladies use the office is especially tricky, historians note. Because the office comes with no set of constitutional duties, it is also a reflection of an individual's style, personality, politics and times.

The Associated Press contributed to this report.