Many poorer states, especially in the South, have always had higher rates of obesity and smoking than states in the Northeast and on the West Coast. Here, a doctor listens to a patient's heartbeat in Jackson, Kentucky.

Don't look now, but America's first Trump-era midterm election could substantially expand Obamacare.

That's right, expand Obamacare – implausible as it sounds after the all-GOP government's near miss on repealing the program and attempts to undermine it. Polls show Democratic calls for improved health insurance continue to resonate with big chunks of the electorate, and may yield Election Day gains.

Specifically, November balloting could bring half the 18 states that have resisted expanding Medicaid, a key feature of the Affordable Care Act, closer to taking that step. If they do, more than 1 million low-income Americans could gain Medicaid coverage.

"I don't think people have put it together," observed Andy Slavitt, a former top Obama health aide. "Election Day is the biggest referendum on the ACA. These votes will also be a referendum on Trump policies, which have done everything they can to limit Medicaid and access to care."

The greatest potential impact lies in two of the three largest states that so far have refused to expand Medicaid despite generous Obamacare subsidies. Democrats Andrew Gillum in Florida and Stacey Abrams in Georgia both back expansion in their competitive campaigns to succeed outgoing Republican governors.

The same dynamic applies in smaller states. In Wisconsin, anti-expansion GOP Gov. Scott Walker trails pro-expansion Democratic rival Tony Evers in his bid for a third term. In Kansas, Maine and South Dakota, pro-expansion Democrats battle anti-expansion Republicans in toss-up gubernatorial races.

At the same time, voters will decide Medicaid expansion for themselves through ballot initiatives in Idaho, Nebraska and Utah. Polls show strong prospects for all three measures, and GOP governors have pledged not to obstruct voters' wishes.

Thirty-two states and the District of Columbia have already expanded, providing Medicaid benefits to more than 10 million low-income Americans, according to the Kaiser Family Foundation. Another 3.7 million stand to gain Medicaid coverage if remaining holdout states follow suit.

"The battleground for Medicaid expansion is in the red states," noted Kaiser health policy expert Diane Rowland. For proponents, the persistent refusal of some GOP leaders makes ballot measures a critical tool.

Those aren't automatic. Maine's outgoing Republican governor, Paul LePage, has blocked Medicaid expansion even after his constituents approved it last year.

Nor does election of a pro-expansion governor ensure that it happens. In North Carolina, the fourth-largest state that hasn't expanded, Democratic Gov. Roy Cooper has been stymied on the issue by Republican legislators since his 2016 election.

In the state, opponents of expansion say the government can't afford it. In Washington, GOP leaders insist Congress must curb the major entitlement programs of Medicaid, Medicare and Social Security to avoid long-term insolvency.

Yet political winds have shifted in the wake of Republican attempts to end Obamacare. In a Kaiser poll this summer, Americans rated the law favorably by 50 percent to 40 percent, after it had remained below 50 percent through Obama's last six years in office.

Both Trump and GOP candidates, under fire over their efforts to eliminate guaranteed, affordable coverage for people with pre-existing conditions, now claim to support that guarantee. In the latest NBC News/Wall Street Journal poll, voters preferred Democrats over Republicans on health care by 18 percentage points.

Democrats have placed the issue at the center of their campaign advertising, to productive effect. In the NBC/WSJ survey, voters ranked health care second behind the economy and jobs as an influence on their votes for Congress; those citing health care back Democrats over Republicans by 69 percent to 22 percent.

In the states the 2018 election has put in play, poor communities across the country stand to gain Medicaid coverage in big chunks: 662,000 in Florida; 388,000 in Georgia; 77,000 in Utah; 74,000 in Kansas; 70,000 in Maine; 41,000 in Idaho; 32,000 in Wisconsin; 31,000 in Nebraska, Kaiser estimates.

"These initiatives are an uprising by the public in state after state against politicians who put their ideology over the health-care needs of their constituents," argued Neera Tanden, another former Obama health adviser. "The public wants people covered."

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