A demonstration in Georgia earlier this year calling for Medicaid expansion. Georgia is one of a few states where the chances of expanding Medicaid could improve, depending on the outcome of Tuesday's gubernatorial elections. (AP Photo/David Goldman)

You won't find Obamacare listed on any state ballots this year, but the future of its coverage expansion will hinge on the outcome of gubernatorial races across the country.

Voters in 15 of the 23 states that haven't expanded their Medicaid programs under the Affordable Care Act will go to the polls on Tuesday, and the outcome of those elections will play a major role in determining the reach of President Obama's health-care law.

Democratic candidates are unanimous in their support for expanded Medicaid programs, which is not mandatory for states, thanks to a Supreme Court ruling in 2012. But a victory for Democratic gubernatorial candidates on Tuesday doesn't guarantee they'll be able to overcome opposition from lawmakers where Republicans control statehouses. Just ask Virginia Gov. Terry McAuliffe, who's now pursuing a much more modest expansion amid continued GOP opposition in his state.

On the other hand, some Republican governors winning re-election on Tuesday could see the political clearance to pursue coverage expansion and the billions of dollars in federal funding that come with it.

Here are the states with especially close races that could soon join the Medicaid expansion, depending on what happens Tuesday.

Maine

The New England state is the most obvious to expand Medicaid if Democratic candidate Michael Michaud is elected. In the past two years, the Democratic-controlled state legislature has sent three expansion bills to Republican Gov. Paul LePage, who's vetoed them all. An estimated 70,000 people would be eligible for Medicaid if expansion takes hold in Maine, which was one of just two states that actually saw the rate of uninsured residents increase last year, according to the Census Bureau.

Florida

Republican Gov. Rick Scott, after voicing surprising support for the Medicaid expansion early last year, has barely made an effort to get the Republican-controlled state legislature to approve it. Meanwhile, former Gov. Charlie Crist (D), now seeking another term, has been a vocal advocate of expanding Medicaid to an estimated 1.3 million people. The state legislature in 2013 examined some alternative Medicaid expansion models, but there hasn't been any movement this year. Crist has floated the idea of using an executive order to force the expansion if state lawmakers don't play ball.

Kansas

The unpopularity of Gov. Sam Brownback's steep tax and spending cuts could put Democrat Paul Davis in the governor's mansion in a deeply conservative state. Davis, the House minority leader, supports Medicaid expansion to an estimated 100,000 residents, but he hasn't made it a central issue in his campaign. If Brownback is voted out, he already put up a barrier to expanding Medicaid in Kansas. He signed a billy earlier this year requiring the state legislature to approve the expansion, eliminating the possibility that Davis, if elected, would be able to act on his own.

Georgia

Like Brownback, Gov. Nathan Deal (R) also signed a bill this year requiring legislative approval of the Medicaid expansion. Deal is locked in a tight race against Democrat Jason Carter, who's been a vocal supporter of expanding Medicaid to an estimated 650,000 Georgians. That's in a state where four rural hospitals have closed in the last two years and more are facing financial challenges. An infusion of federal funds from the Medicaid expansion could provide a lifeline to these hospitals, supporters of the expansion say. That's why there's some thought in Georgia that Deal, if re-elected, could try to put forward an expansion plan, though he's still speaking out against it in the final days of the campaign.

Wisconsin

Gov. Scott Walker (R) carved out a unique path when he rejected Medicaid expansion funds last year. He pared back the state's generous Medicaid eligibility standards but also ensured that everyone earning below the federal poverty level could enroll in the program.  That meant an estimated 97,000 additional people were eligible to enroll in Wisconsin's Medicaid program, but about 62,000 people with income above the poverty level were dropped from Medicaid coverage and sent to ACA health insurance marketplaces to purchase subsidized coverage.

As of July, just about one-third of those former Medicaid enrollees had signed up for new marketplace coverage. Walker's Democratic challenger, Mary Burke, has been a fervent critic of his decision to eschew enhanced federal funding for the Medicaid expansion. If elected, though, Burke would likely need the support of the Republican legislature to take a more traditional Medicaid expansion path.

Other states to watch

Incumbent governors Bill Haslam of Tennessee, Dennis Daugaard of South Dakota, and Matt Mead of Wyoming — all Republicans — are expected to cruise to re-election victories on Tuesday, and each has expressed an interest in crafting plans that would let their states accept Medicaid expansion funding. With re-election behind them, 2015 could be the year these governors — and others — feel like it's safe enough, politically speaking, to push for the expansion.