The Affordable Care Act, or Obamacare, allows states to expand the Medicaid healthcare program to people making up to 138% of the federal poverty limit.

Three states have questions on the ballot in Tuesday's midterm elections that would expand Medicaid: Idaho, Nebraska, and Utah.

Six other states — Florida, Georgia, Kansas, Maine, South Dakota, and Wisconsin — have Democratic candidates for governor on the ballot that would expand Medicaid access.

According to healthcare consulting firm Avalere, up to 2.7 million people could gain access to coverage on Tuesday.

Tuesday's midterm elections not only will determine the control of Congress and dozens of governors' mansions across the US. It could decide access to healthcare for millions of low-income Americans.

The Affordable Care Act's Medicaid expansion, which allows low income Americans making up to 138% of the federal poverty limit to get access to the program, will be on the ballot in three states. And six other states that have not expanded the program have pro-expansion governor candidates on the ballot, as well.

According to Avalere Health, a healthcare consulting firm, up to 2.7 million Americans could gain access to healthcare if the results break a certain way. In three states — Idaho, Nebraska, and Utah — Medicaid expansion is directly on the ballot, while six other states that have not expanded Medicaid have Democratic, pro-expansion governor candidates in competitive races.

"In states with competitive gubernatorial races, many candidates are making Medicaid expansion a key differentiator," Elizabeth Carpenter, senior vice president at Avalere, said of the possible expansions. "Depending on the election results, we could see Medicaid expansion on the agenda again in states across the country."

Here's a breakdown of how many people could gain access to healthcare in each state if the pro-expansion result comes through:

Florida (governor race): 1,343,612

Georgia (governor race): 690,162

Kansas (governor race): 136,423

Maine (governor race): 48,382

South Dakota (governor race): 45,293

Wisconsin (governor race): 140,774

Idaho (ballot question): 92,439

Nebraska (ballot question: 97,937

Utah (ballot question): 134,756

Medicaid expansion has become more popular over the years, even in deep red states, making it a strong issue for many Democratic candidates. A February poll by the Kaiser Family Foundation, a nonpartisan health policy think tank, found that 56% of people in non-expansion states wanted to expand Medicaid, while just 37% were against it.

Another poll in October from Kaiser found that 49% of people said they were more likely to vote for a candidate if they supported expansion, while just 28% said it made them less likely to vote for a candidate.

Andrew Gillum in Florida, Stacey Abrams in Georgia, and Billie Sutton in South Dakota have all used their support for Medicaid expansion as key planks in their campaigns.

Read more: The 2018 midterms will have a big impact on healthcare, from Medicaid to nurses to abortion»

This isn't to say that the program would be expanded immediately if results go a certain way: State legislatures could stymie the expansion, as Virginia's legislature did for years despite the state's Democratic governor's wishes. Maine also voted to expand the program in 2017, but departing Gov. Paul LePage refused to expand the program.