“We’ve been going to malls, drugstores, churches, community halls, Walmarts — you name it,” says Stacey Carter, Humana’s sales director for Mississippi. “Sometimes it’s a gas station, because out in the rural areas, that’s where people congregate. A lot of them don’t have Internet, so the Wi-Fi is essential. But education has been the first priority. Most of the uninsured don’t know they might be eligible for government subsidies.”

Mississippi is the poorest, sickest state in the nation, and most insurance companies have avoided it, preferring to do business in more profitable markets. In 36 of Mississippi’s poorest counties, no insurance companies were offering plans that meet ACA guidelines until the Obama administration intervened and asked Kentucky-based Humana to help fill in the gaps . Humana had two of these buses built to spread awareness and drum up business. They’re zigzagging around the state on a tour called Covering Mississippi. So far they’ve traveled 7,000 miles, and the agents have seen more than a thousand people.

JACKSON, Miss. — A custom-built bus with oversize windows is parked outside a health fair at the University Medical Center. The decal on its side reads, “Making healthcare reform transparent.” Inside the bus are snacks, Wi-Fi and three booths where sales agents from the Humana health insurance company sit behind laptops and explain the Affordable Care Act to uninsured people. They sign up customers too.

The new exchanges, or health care marketplaces, were supposed to promote competition between insurance companies, driving down premiums and smoothing the path for the uninsured. In Mississippi, market economics have produced the opposite effect. Only two insurance companies are participating in the exchange here, and their premiums are among the highest in the nation, with silver plans averaging $448 a month, or $1,069 for a family of four . In 78 of the state’s 82 counties, only one insurance company is offering ACA plans.

Nowhere else in America has a greater need for affordable, accessible health care. Mississippi has the lowest life expectancy in the country , the highest rates of obesity and diabetes, and an infant mortality rate closer to Sri Lanka’s and Botswana’s than to the rest of the United States’. Heart disease is epidemic , and nearly 20 percent of the state’s population — some 511,000 people — were uninsured when President Obama signed the Affordable Care Act last March.

Others aren’t so lucky. Some people making $35,000 a year are looking at a $400 a month premiums with a $6,200 deductible. If they lived in another state, the same plan through the same company would be far cheaper.

She turns her screen to show Taylor the results. Thanks to a subsidy from the federal government, a silver plan will cost him only 55 cents a month, with a $95 deductible. All he has to do is click “accept” on the email that she’s sending him and pay the first 55 cents by bank card or money order. Taylor doesn’t have a computer, but he gets email on his phone. She asks him to check the phone now and he says, “Need to put some credit on that one. But I’ll do it. Fifty-five cents a month? So far, so good.”

Chris Taylor, a 58-year-old Walmart employee, climbs aboard the bus because he’s heard that health insurance is now mandatory. He’s never had insurance before and can’t remember the last time he went to a doctor. Humana sales agent Ezsma Holmes welcomes him into a booth. She spends about 20 minutes asking him questions and entering the information into her laptop. Then she hits “save and continue” for the final time, taps her fingernail for a few moments and breaks into a smile.

Spencer Bowley, a 24-year-old health care navigator at the Jackson University Medical Center, meets them almost every day. “They’re the working poor, basically,” he says. “They’re making $7,000 a year, and they’re seeing premiums of $500 a month, with really high deductibles. If they were making less, they’d qualify for Medicaid. If they were making over about $11,500 , the government subsidies would kick in.”

When the ACA was written, the law required all the states to expand Medicaid. Low-income people who weren’t poor enough to get existing Medicaid would be covered. Then the Supreme Court decided that states had the right not to expand Medicaid. Mississippi, led by Republican Gov. Phil Bryant, who has described “Obamacare” as “an assault on the liberty of American citizens,” was one of two dozen states to exercise this right. That left an estimated 300,000 Mississippians with no prospect of health insurance.

Democrats, moderate Republicans and many doctors and hospitals have called on Bryant to rethink his decision, expand Medicaid and collect the billions of federal dollars that would flow into the state. One study done by the Mississippi Health Advocacy Program found that expanding Medicaid would generate $14 billion in economic activity and create 20,000 new jobs by 2020. For the first three years, the federal government pays all the costs of expanded Medicaid. After that, the government pays 90 percent. But Bryant says he doesn’t trust the federal government to honor its commitment and adds that Mississippi can’t afford the 10 percent in any event. The state already has 640,000 people on Medicaid. Another 300,000 would mean close to a million people on Medicaid, nearly a third of the state’s population. Bryant says that expanding Medicaid would remove the incentive for the poor to work their way up to a higher income bracket.

However, pressure is building on the governor to expand Medicaid or work out some public-private solution. That’s what happened in Arkansas, which uses Medicaid funds to pay private insurance plans for low-income residents. The pressure is likely to build further in April, when those 300,000 people face their first $95 penalty for not having insurance. Republican governors in Utah, Arizona and Florida have decided to expand Medicaid in their states, despite their opposition to “Obamacare.” Jake McGraw, a policy analyst and editor of the Rethink Mississippi website, believes the Magnolia State will one day do the same.

“We’ll probably be the last state in the country to do it, and it will definitely make a huge difference,” he says. “But Mississippi has also exposed a key structural problem in the ACA: The poorest, sickest counties in America are generating the highest premiums, because they’re a bad bet for insurance companies.”