(CNN) As Ady Barkan has struggled with the deterioration of his body as a result of ALS, the activist has pulled off a feat that would be remarkable even for the most agile of health care advocates.

This year, month after month, he has drawn most of the major presidential candidates to his doorstep and championed "Medicare for All" while forcing the presidential contenders to think through the impact of their health care agendas in the most personal terms.

He brought California Sen. Kamala Harris to tears recalling the day her mother was diagnosed with colon cancer. Massachusetts Sen. Elizabeth Warren used Barkan's case to punctuate the failures of the healthcare system during a July presidential debate: "Ady has health insurance, good health insurance, and it's not nearly enough," she said.

Barkan and Vermont Sen. Bernie Sanders, the author of the Medicare for All legislation, discussed their legacies during their conversation, which was posted online in early September.

"In terms of your legacy, Ady," Sanders told Barkan, "I think it will be very clear that even with the terrible illness that you're struggling with right now, that you didn't give up, that you understood that -- especially given your illness -- that you could play a significant in rallying the American people toward a sane and humane health care system."

In the latest interview released Thursday with Pete Buttigieg , the South Bend, Indiana Mayor told Barkan that it was the first time he'd been around breathing equipment since the death of his father, who had cancer, in January.

"We sat down with a social worker who basically explained to us at the hospital that in terms of long term care our best option was probably for our family to spend down everything that we had until we were asset-poor enough to qualify for Medicaid," Buttigieg told Barkan, according to the transcript shared with CNN. "I remember just thinking, is that how this works in America?"

The two debated their differing views on Medicare for All, and Barkan told Buttigieg he appreciated that the mayor was "willing to have the tough conversations even when someone doesn't agree with you."

In their exchange, Barkan called out former Vice President Joe Biden, who Barkan says is the only top-tier presidential candidate who has not responded to his invitation to meet.

On September 18, he issued a searing plea to Biden, noting that Biden has his own heartbreaking struggles involving the healthcare system (most recently with the death of his son Beau in 2015 from a brain tumor).

"Mr. Vice President you know about illness. You know about doctors and hospitals. You know that health care is personal. ... You won't come talk to me about it?" Barkan said in video missive to Biden the day before undergoing surgery for a tracheostomy to help him breathe. "Look a dying man in the eyes and tell me how we fix this country."

In an interview with CNN this month, Barkan described ALS as "the story of things becoming impossible" -- from a simple stroll around the neighborhood to his ability to tickle his 3-year-old son Carl. ALS, or amyotrophic lateral sclerosis, is a neurodegenerative disease that affects the nerve cells in the brain and spinal cord, ultimately depriving the brain of its ability to initiate and control muscle movement, including the loss of speech. (Barkan now speaks through a computer).

"It's exhausting and overwhelming," Barkan told CNN. "For me, ALS has been a lesson in exactly how broken our health care system is and why it's so important to fix it."

In this family photo, Barkan is pictured with his wife Rachael and son Carl in October 2016.

Barkan, a life-long advocate on economic justice issues who was diagnosed with ALS in October 2016, has imparted those lessons not only with high-profile testimony in Washington, but also in these intimate one-on-one conversations with candidates.

He and his crew film publish the interviews as part of the work of their PAC, the Be A Hero fund, which attempts to hold politicians accountable on health care and other issues by using the stories of average Americans as their persuasion tool.

Barkan realized the power of his exchanges with politicians when he met former Arizona Sen. Jeff Flake by chance in December 2017 on an airplane. Overwhelmed by his mounting medical bills, Barkan urged Flake not to support the GOP tax bill, which he believed would disrupt his health care coverage. "You can save my life," Barkan told Flake in a n exchange captured by a fellow passenger . "Please remember this conversation." Flake did end up voting for the tax bill -- in contradiction to Barkan's request -- but that exchange vaulted Barkan into the national spotlight.

As Barkan has explained to the current crop of presidential candidates, his insurance company tried to deny coverage for a breathing assistance machine that he needed to live. He said he, his wife Rachael, an assistant and a lawyer spent "endless time on the phone trying to get our insurance company to behave properly, lawfully. Beyond that, his family is billed $20,000 a month out of pocket for the 24-hour home care that he needs.

"I'm lucky to have wealthy supporters cover the cost for us, but that's not an option for a lot of people -- most just go bankrupt," he told CNN, which provided questions to Barkan ahead of time to give him enough time to write out answers.

"Ninety percent of Americans with ALS choose not to go on a ventilator because it requires 24-hour care, which most insurance plans don't cover. In Japan, where long-term care is guaranteed, the numbers are reversed. That just isn't right, and it doesn't need to be this way."

That view has fueled Barkan's advocacy for Medicare for All, the signature health care proposal from Sanders: "I've come to believe that fundamentally we need radical, disruptive change to the status quo," he said. "The only plan I've seen that aims for that level of ambition is Medicare for All."

He believes that any plan that stops short of the promise of Medicare for All -- the kinds of plans that have been proposed by Buttigieg, Biden and Minnesota Sen. Amy Klobuchar, for example — "won't deliver the universal coverage or the cost savings that we need."

Barkan testifies before the House Rules Committee at a hearing on a "Medicare for All" bill on Capitol Hill in April 2019.

Barkan, who gets around in a wheelchair, speaks through a vocalizer and takes his meals through a feeding tube in his stomach, has still managed to make his sense of urgency felt through in-depth conversations with Buttigieg, Sanders, Harris, Warren, New Jersey Sen. Cory Booker, and Julián Castro, the former Secretary of Housing and Urban Development under President Barack Obama.

He says Klobuchar, former Texas Rep. Beto O'Rourke and businessman Asndrew Yang have also agreed to meet with him. The Be A Hero PAC has started a petition calling on Biden to meet with Barkan. Biden's team did not respond to CNN's query about why the former vice president has not responded to Barkan's invitation.

But Barkan isn't giving up on his hope for a one-on-one with one of the 2020 race's front-runners.

It's a persistence that New York Rep. Alexandria Ocasio-Cortez notes in the prologue she wrote for his new memoir, "Eyes to the Wind."

Even through his vocalizer, Barkan's testimony to Congress "forced an urgency and moral clarity that members could not look away from or ignore," Ocasio-Cortez wrote.

"I saw their discomfort at issuing the usual excuses, and Ady also would not tolerate them—even with many physical capabilities gone," Ocasio-Cortez wrote.

The New York Democrat first met Barkan when he stopped by a labor town hall that she was holding at a church in the Bronx after winning her primary election last year. He could still speak at that point and she held the microphone for him as he addressed the crowd.

They met again this year, at her congressional office after the his testimony to Congress.

Barkan acknowledges that part of the power of his advocacy is that he is dying from ALS, a fact he points out in his Twitter profile. He told CNN he is "trying to use the time I have left here to make things better for as long as I still can."

"If I could be healthy and completely anonymous, I would do it in a heartbeat," he said. But because of his illness, his activism with Be a Hero and the Center for Popular Democracy have drawn national notice. His team went on to travel the country making health-care ads that he said were among the top-performing spots of 2018.

"We built a platform that made it hard for candidates to ignore us," Barkan said. "There are millions of folks who the candidates should sit down with. I'm just hoping I can be a voice for them and force candidates to answer questions that really matter to people."