Gov.-elect Janet Mills of Maine, the state’s first female governor, has vowed to expand Medicaid her first day in office. (Robert F. Bukaty/AP)

Citizen power propelled the biggest expansion of Medicaid in heavily Republican states since the early years of the Affordable Care Act, with hundreds of thousands of poor and vulnerable residents standing to gain health coverage as a result of Tuesday’s elections.

Voters in Idaho, Nebraska and Utah approved ballot initiatives to include in their Medicaid programs adults with incomes of up to 138 percent of the federal poverty line. The results accomplish a broadening of the safety-net insurance that the states’ legislatures had balked at for years.

In addition, Maine voters elected Democrat Janet Mills as governor, clearing the path for a Medicaid expansion that voters approved by referendum a year ago. The outgoing GOP governor, Paul LePage, has been an ardent foe of the expansion and had blocked it for a year, leading to a court battle.

Mills has said she will expand the program on her first day in office.

On Wednesday, Montana officials were still tallying the results of the nation’s fourth Medicaid ballot initiative, which appeared as if it might narrowly fail. The state expanded Medicaid two years ago temporarily, due to end next summer. The initiative would make the expansion permanent and add a cigarette tax of $2 per pack to pay for the state’s share.

After Mainers put to voters in 2017 the question of the proper scope of Medicaid, the grass-roots tactic spread quickly to other red states in which health-care-minded residents and activists, supported by significant outside funding on both sides, gathered signatures to force the issue onto the ballot in an effort to circumvent years of resistance by conservative legislatures.

With all three expansion initiatives passing Tuesday, in a year in which health care loomed large as an election issue, longtime proponents of the ACA, which allowed the expansion, were elated Wednesday.

“This election proves that politicians who fought to repeal the Affordable Care Act got it wrong,” said Jonathan Schleifer, executive director of the Fairness Project, a three-year-old Washington-based nonprofit that was the biggest funder, spending more than $6 million on such activities as polling, signature gathering and advertising. “Expanding access to health care isn’t a blue-state value or a red-state value; it’s an American value.”

Schleifer and Topher Spiro, vice president for health policy at the Center for American Progress, said on a conference call that they plan to look for grass-roots partners in other non-expansion states that allow ballot initiatives, possibly Florida, Oklahoma, Missouri and Mississippi.

Idaho’s Proposition 2 won particularly strong support, with 62 percent of the vote. That initiative, predicted to extend Medicaid to 62,000 Idahoans, drew a surprise endorsement last week from the state’s outgoing governor, C.L. “Butch” Otter (R), who said that reducing the number of uninsured Idahoans would have a ripple effect of stabilizing struggling rural hospitals and public health clinics.

Nebraska’s Initiative 427, estimated to make 87,000 poor residents eligible for Medicaid, passed with 53 percent of the vote. For six years, the state legislature had rejected expansion bills.

In Utah, Proposition 3 passed with 54 percent of the vote and is expected to enable 150,000 residents to qualify for Medicaid.

Utah Gov. Gary R. Herbert (R) signed into law in 2016 a bill that allowed a minor expansion, focused on a few thousand people who are homeless or need treatment for addictions. This year, he signed into law a partial expansion — to make eligible people with incomes of up to the poverty line — even though federal officials have not allowed such halfway steps. The ballot initiative will overtake that partial expansion.

The effects of Tuesday’s votes will lower from 18 to 14 the number of states that have not expanded their Medicaid programs to low-income people with slightly higher incomes. The outstanding states, primarily in the South and Midwest, contain an estimated 2.2 million residents who would be eligible to join Medicaid in an expansion, according to a recent analysis by the Kaiser Family Foundation.

The checkerboard of states that have broadened Medicaid is the effect of a wrinkle that the Democratic authors of the ACA never anticipated when they pushed the 2,000-page statute through Congress in 2010.

At the outset, the law for the first time created a uniform federal standard for who can join Medicaid, rather than leaving that decision largely to states. It said that adults without minor children could enroll nationwide, and it set the 138 percent income threshold — $16,753 for an individual and $34,638 for a household of four.

The original idea was that, when the expansion began in 2014, Medicaid would account for about half of a large insurance increase the ACA was intended to bring about, with insurance exchanges for Americans who cannot get affordable health benefits through a job achieving the rest. However, in a case challenging the law’s constitutionality, the Supreme Court in 2012 upheld the ACA but ruled that each state could decide whether to expand Medicaid.

From the start, Republican opposition has centered on the fraction of the expense of expansions that falls on states. For the first three years starting in 2014, the federal government covered the entire cost of insuring the additional Medicaid recipients that the law made eligible. Federal money covers 94 percent of the cost and is scheduled to taper off to 90 percent in 2020.

Expansion proponents counter that it brings additional federal money into states, while diminishing the number of poor uninsured residents unable to pay hospital or doctors’ bills.

Since the expansion began, researchers have been examining its effects. Studies consistently show that the rate of uninsured people has dropped further in expansion states. And despite shortages in some areas of doctors willing to treat people on Medicaid, studies have shown that expansion is associated with improved access to care, including to treatment for mental-health disorders and opioid addiction. Compared with non-
expansion states, those with more-generous Medicaid programs tend to have fewer infant deaths, and cancers are detected earlier.