Nashua, New Hampshire — Hours before Senator Bernie Sanders returned to his Burlington home Saturday to recover from a heart attack, Carmen Yulín Cruz, the mayor of the Puerto Rican capital of San Juan, campaigned through New Hampshire in his place. At a town hall in Nashua, the mayor pointed out what she called the "elephant in the room."

"He's a very serious guy," Cruz paced the pews of the Unitarian-Universalist Church of Nashua. "You may want him to laugh a little every once in a while. But this is not a Miss Congeniality contest. This is about life and the essence of who we are."

Yet cheers lifted to the church vaults as the larger elephant was addressed. "By the way, he's fine. I spoke to him yesterday. He's rather ticked off that he's off the campaign trail. But he's had our back, and now we have to have his," Cruz remarked before sliding into a Spanish translation.

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Sanders was admitted to Desert Springs Hospital Medical Center in Paradise, Nevada, on Tuesday after suffering chest pains. His diagnosis, described by the campaign as "blockage in one artery" was revealed three days later to be "a myocardial infarction," the medical name for a heart attack.

Carmen Yulin Cruz and Bernie Sanders in Puerto Rico in 2017. ANDRE KANG / AP

Asked if the delay in diagnosis proved a point of concern, Cruz shook her head. "If there was something to be concerned about, he would have been open with the American people," she said. "Because he wants most from us, is to have that new relationship that a person who is in public office should have. Not one of being deceitful like President Trump. Not one of lying, like President Trump. But one of honesty and integrity."

The longtime Vermont lawmaker told reporters Saturday he was "happy to be home" before joining family inside his Burlington residence.

Cruz recounted that the senator had "strength in his voice" while speaking with her over the phone Friday. "Those are just things you cannot fake," she added.

The Puerto Rican gubernatorial candidate told CBS News that Sanders' was more concerned about her health, having spent time in the hospital a few weeks ago for the flu. "He actually called, believe it or not. I was in the hospital two weeks ago. I had the flu and got severely dehydrated. He was calling to see how I was doing. And making sure if I was okay and asking to see if I had any questions about this weekend in New Hampshire."

In 2017, it was a telephone call from Sanders that first convinced the mayor to support him. Sanders reached out personally to plan a tour of San Juan in the aftermath of Hurricane Maria. Cruz joked she did not believe it was him on the other line.

"He's never going to tell you this. So I'll tell you a little secret. I hung up on him," Cruz quipped. "I can't say it, because there are children and we're in a house of God, but I was like—" The mayor mouthed the word, "bullsh**," triggering laughter throughout the church.

Sanders' trip to San Juan in October 2017 resonated with the mayor who witnessed Hurricane Maria's wrath first-hand. "There he was. No cameras. No press. No posturing. Just Bernie," she said. Cruz backed Hillary Clinton in the 2016 presidential primary contest.

At a canvassing kick off in Manchester, the surrogate hugged each and every volunteer corralled in Sander's mural-adorned field office. She repeated the mantra of the Sanders campaign several times over: "Not me. Us."

Carmen Yulin Cruz campaigns in Nashua, New Hampshire on October 5, 2019. Nicole Sganga

Yet in a defense of his health, the Puerto Rico politician conceded it is "a little bit" about Bernie Sanders. "He's fine. And a lot of people are going to tell us that he's not," she cautioned volunteers. "He says, 'It's not me, it's us.' But it's a little bit about him. He's the glue that brings us all together."

In a candid presentation, the mayor rehearsed canvassing scenarios with doorknockers' anticipating voter concerns about socialism or "free stuff."

"Let's not look at the Republican label, that talking point," Cruz told organizers. "Do you want to be able to send your children to college and know they'll have a life afterwards? Do you want to be able to get sick and not go bankrupt?"

In a final pitch to canvassers, Cruz launched an attack of the media narrative around polling, she says mischaracterizes Sanders' movement. "They concentrated on Warren's surge. Well hell, you can surge all you want," Cruz said, citing the Sanders' record-breaking fundraising numbers, $25.3 million between June and the end of September.

The Senator was formerly scheduled for a New Hampshire swing next weekend, with meetings and at least one public event scheduled October 12 and 13. An organizer with the New Hampshire Youth Movement tells CBS News Sanders still plans to attend The People's Presidential Forum at the University of New Hampshire in Durham on Sunday. The Sanders campaign has announced only that the candidate will return to the trail in time for the Democratic debate on October 15.

At the close of her Nashua town hall, Cruz wrapped remarks with a rendition of Christina Aguilera's "Beautiful." The San Juan mayor belted the chorus. "Words can't bring you down," her voice fluttered.

"Bernie will finish this fight," Cruz said at last. "All he needs is you."