The fate of Medicaid expansion, a central tenet of President Obama's signature health-care legislation, is in the hands of the people in several states.

In Idaho, Nebraska and Utah, voters will decide whether to make more low-income people, those up to 138 percent of the federal poverty line, eligible for Medicaid, the government-run health insurance program. In most of the other states, who voters elect as governor and to the legislature will influence the direction of this health-care policy for years to come.

Since the Affordable Care Act passed in 2010, 33 states have expanded Medicaid, largely along partisan lines, with Republicans leading the holdout movement. But in some cases, Republican governors tried for years to convince their GOP legislatures to expand. 

Health policy experts say that, generally, a state's status of expansion guides which races are most important to watch in the midterms.

"For a state that hasn’t yet expanded, the governor can’t do it all, so you have to watch what happens with the legislature," says David Jones, associate professor of health law at Boston University who recently examined where Medicaid expansion appears more vulnerable. "But for states that have already expanded, the legislature doesn’t matter as much" because the governor has authority to tweak the current law or to end expansion in some cases.

The midterms come at a crucial time for health care. The Trump administration gave states the greenlight to adopt new rules for Medicaid that the Obama administration rejected. For instance, Arkansas, Kentucky, Indiana and New Hampshire have been approved to add work requirements, and several other states have applied. In July, a federal judge struck down Kentucky's work requirements plan, putting the rest of the states' policies into legal jeopardy. Despite the ruling, the Trump administration has signaled that it plans to proceed with work requirements.

Michigan is one expansion state where health policy could veer far to the right if the Republican nominee for governor, ‎Bill Schuette, wins what is considered a tossup race. Schuette, the state’s attorney general, leans more conservative than term-limited Republican Gov. Rick Snyder. On the campaign trail, Schuette has supported repealing and replacing the Affordable Care Act.

"He talks a lot about what he doesn’t like [about the ACA], but he has yet to say what he’d do that’s positive," says Marianne Udow-Phillips, executive director of the Center for Healthcare Research and Transformation based in Ann Arbor, Mich. "I see him being in the mold of Scott Pruitt at the Environmental Protection Agency, doing a lot of rolling back of regulations."

In Michigan, 680,000 people gained coverage under Medicaid expansion, and 350,000 could lose it if work requirements are put in place. Snyder signed a bill in June to submit a waiver to the federal government that, if approved, would require Medicaid recipients in the state to have a job.

"We’ve gotten used to thinking that Michigan is a moderate state because they have Democratic senators and sometimes go blue in presidential elections," says Jones, "but ... it's a pretty conservative group of senators in the statehouse," and a more conservative governor might be able to drum up support for far-right Medicaid changes.

Schuette's Democratic opponent, Gretchen Whitmer, supports Medicaid expansion and opposes the work requirements waiver, according to a spokesperson in her campaign office.

In Ohio, another expansion state, GOP Gov. John Kasich is term-limited. While he is one of the staunchest defenders of Medicaid expansion, he did pass off a waiver request for work requirements to the feds. Republican Attorney General Mike DeWine and Democrat Richard Cordray, the former head of the Consumer Financial Protection Bureau, are in a tossup race to succeed him.

DeWine leans more pragmatic in general, so John Corlette, executive director of the Center for Community Solutions based in Cleveland, says "I would expect his approach would be closer to Kasich." DeWine has said he supports expansion with a work component, while Cordray supports expansion with no work requirements.

In Ohio, work requirements threaten coverage for 36,000 adults.

If any states elect governors who are more conservative than their predecessors, "Kentucky is a good example of what a change in leadership can mean for Medicaid expansion," says Jones. There, a Democratic governor expanded Medicaid to 500,000 Kentuckians. When Republican Matt Bevin was elected in 2015, he added work requirements, along with premiums and reporting income changes.

A governor's authority, however, isn't limitless. Since residents in Maine voted in favor of expansion last year, GOP Gov. Paul LePage has refused to enact the policy. The state's Supreme Court last week ordered him to move forward with expansion.

Implementation of it, though, will likely fall to his successor. LePage is term-limited. Running to take his place is Democratic Attorney General Janet Mills, who supports expansion. Republican challenger Shawn Moody, a business owner, is following LePage's lead and opposing it. If the state expands Medicaid per the court's orders, 70,000 people would gain coverage.

Among states that haven’t expanded Medicaid, Jones says the state to watch is Kansas. In 2017, the legislature passed a Medicaid expansion bill, but then-GOP Gov. Sam Brownback vetoed it. The legislature narrowly missed getting enough votes to override him. 

While it’s unlikely that the legislature in a state that deep red would flip Democrat, "the state seems to be trending more moderate," says Jones. On a recent trip to Topeka, he says "many Republicans were willing to say they would support Medicaid expansion. They saw it as a way to save their rural hospitals."

The governor's race in the state is a matchup between hardline conservative Secretary of State Kris Kobach and Democratic state Sen. Laura Kelly. Kobach has a slight edge. Kelly has vowed to expand Medicaid, and Kobach is opposed to it.

While it's a wild card, the political landscape in Florida has the potiential to completely shift in November, laying the groundwork for the state to expand Medicaid. Despite support from GOP Gov. Rick Scott, who is running for U.S. Senate, the GOP-controlled legislature has rebuffed all expansion efforts over the years.

Now, Democrats have a real shot at taking control in the Senate. While it's unlikely they'll take control of the House, they are expected to gain ground. The governor's race is between Tallahassee Mayor Andrew Gillum, who supports the Democratic Socialist platform of "Medicare for all." His opponent, Republican Congressman Ron DeSantis, is against expanding Medicaid.

"Supporters of the ACA think of Florida as the holy grail in terms of expansion," says Jones.

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*This has been updated to reflect Gretchen Whitmer's opposition to Medicaid work requirements.