Hours before the first debate of the 2020 Democratic primary, Bernie Sanders was preparing in a hotel conference room in Miami. He pored over briefing books and talked strategy with his aides.

Then he got on the phone with Cardi B.

At one point during his FaceTime conversation with the rapper, Sanders posed a personal question: “How is motherhood?”

"Motherhood is good,” Cardi B, who has a 1-year-old daughter, replied. “But it’s tough when you're an artist. It's like a whole two lives that you have to balance out.”

The fact that Sanders chatted about parenting with Cardi B in the moments before one of the most important events in the presidential race is a testament to the oddball alliance the two have developed over the past year. It’s a friendship and political partnership that's drawn the attention of millions of people: Since Sanders and Cardi B unveiled a videotaped conversation this month that they had at a nail salon in Detroit, it has racked up a stunning 22 million views on their social media accounts. That’s more than the 18 million-plus people who tuned into the second night of the June primary debate across three networks, which was the most-watched such event in history.

Cardi B, in other words, might be one of Sanders’ most powerful political allies, which makes their unexpected bond even more intriguing. Her social media might also underscore why Sanders has taken care to court the popular musician. According to interviews with Sanders’ aides, as well as excerpts of their private FaceTime conversation obtained by POLITICO, their friendship is based on shared progressive ideals, a favorite former president, and a similar devil-may-care attitude.

“She’s a no-B.S. person,” said Ari Rabin-Havt, the chief of staff for Sanders' presidential campaign. “And Bernie Sanders loves no-B.S. people.”

Cardi B backed Sanders when he ran for president in 2016. “Vote for Daddy Bernie, bitch,” she told her fans in a video. But the endorsement escaped the candidate's notice then. According to his aides, Sanders didn’t know who she was until they shared a viral moment in 2018. Cardi B told GQ that Franklin D. Roosevelt was “the real ‘Make America Great Again,’ because if it wasn’t for him, old people wouldn’t even get Social Security.”

Sanders’ team responded on Twitter: “Cardi B is right. If we are really going to make America great we need to strengthen Social Security.” The tweet racked up tens of thousands of retweets and likes, so Sanders decided to capitalize on the sensation, recording a video in his Senate office drawing more attention to Cardi B’s comments.

“I remember him walking around saying, ‘I can’t believe this is as big as it is,’” said Josh Miller-Lewis, Sanders’ digital communications director. “He talks about Social Security every single day and it’s never on the front page of anything. So to have an opportunity to talk about expanding Social Security and have it mentioned on every music blog in the country and ABC is writing about it and everyone else — that’s a huge victory.”

Cardi B, 26, and Sanders, 77, have spoken on the phone or in person three times in recent months, according to his aides. When they chatted on FaceTime — the call lasted five to 10 minutes — they discussed the possibility of recording a talk together and releasing it online.

The night before they taped the video in July, they met for the first time at a hotel conference room in Detroit. This time, Sanders was getting ready for the second debate. Sanders and Cardi B had planned to get together for about 15 minutes, but ended up chatting for about 40 minutes, according to a person familiar with the meeting. There were no aides or handlers present, just their bodyguards, the person said.

Sanders and Cardi B share a love of FDR, whom Sanders has repeatedly tried to tie himself to during his campaign. His staffers also said he's impressed by Cardi B’s intelligence and interest in pushing young people to get engaged in politics. Cardi B has said she wants to “build a movement of young people to transform this country” and has solicited her followers on social media for ideas about what to ask Democratic presidential candidates.

“He is really struck by how smart she is,” said Rabin-Havt. “He’s repeatedly remarked about how she’s a genius ... He’s commented, ‘You can see some people are just observing everything and understanding and deeply connecting to things.'”

Cardi B is right. If we are really going to make America great we need to strengthen Social Security so that seniors are able to retire with the dignity they deserve. https://t.co/B8cOkoOdLc — Bernie Sanders (@SenSanders) April 18, 2018

Cardi B has urged her fans to watch the 2020 debates. During their FaceTime chat, Sanders and Cardi B talked about the Night One of the first primary debate, as well as President Donald Trump’s response to it.

"Yesterday, the Democratic debate was going on, and I just got so upset with Trump tweeting out ‘boring’ because it's just — this is not a reality show,” Cardi B said. “This is not supposed to be fun. This is not supposed to be entertainment.”

“That’s absolutely right,” Sanders replied. “This guy himself has created massive problems, and you know, I look forward on my first day as president to issue executive orders undoing the problems that he did."

They also discussed Sanders’ plan to wipe out student loan debt. Cardi B grew up in poverty and struggled to get by in college.

"I think this is the best thing to do,” Cardi B told Sanders. “A lot of people drop out of colleges and don't attend college because they can't afford it, like me. When I was going to a college in the city, I could not afford transportation, food. I was just stuck in the city for hours without eating until my next class."

"Yup,” Sanders said. “You got a whole lot of people who even drop out of college because they can't afford it. Then they're still stuck with a lot of debt that they're still paying off their whole lives ... And my argument is: We're going to pay for that by a tax on Wall Street. The American people bailed out Wall Street, you remember, 10 years ago. Well, it's Wall Street's time to help the working class of this country."

Thanks to @iamcardib for calling attention to the importance of Social Security. pic.twitter.com/bJdt9Oxzzf — Bernie Sanders (@SenSanders) April 18, 2018

Cardi B, who's worth millions, said: "Well, I'm not involved in Wall Street, so that's fine with me!”

Celebrity endorsements come with risks: In 2016, Hillary Clinton trounced Trump among the Hollywood set, which made her look out of touch to some voters even as it helped her raise vast sums of money. Sanders isn't courting celebrities anywhere close to the degree Clinton did. But he has sought to make inroads among superstars of color, including by having a private lunch in Hollywood last month with black and Latino musicians, artists, social media names and others.

To overtake Joe Biden and beat back Elizabeth Warren, Sanders needs to perform better with black Democrats and hold on to his youth support. Biden is polling first among black voters, with Sanders typically posting a distant second in surveys. At the same time, Warren has outperformed Sanders among young voters in a handful of recent polls.

According to Sanders’ advisers, turning out people who don’t usually vote is also critical to his success. That's a constituency Cardi B could potentially tap into.

“Bernie’s whole political project is about bringing people into the political process who might not otherwise be interested,” Miller-Lewis said. “A lot of these people are not watching MSNBC. They’re not watching CNN. They’re maybe not tuning into politics at all. They’re going on Instagram 30 minutes a day. So finding people where they are and not going on the normal TV news circuit is a very important part of his strategy.”