Republicans in Congress are waiting with bated breath for the moment when they pass a repeal of the Affordable Care Act in 2017 and President-elect Donald Trump goes to sign it, but it’s their colleagues back in their home states that may have the most to lose from scrapping the law.

The repeal plans congressional Republicans have floated wouldn’t likely take effect until 2019 or 2020. But already, governors and state legislatures are voicing concerns that repealing the ACA may leave millions of people uninsured, as well as take away some of the mechanisms that helped their states drastically slash their uninsured rates.

At the top of their list of concerns is the fact that the most likely blueprint in Congress for repeal, a 2015 bill that President Barack Obama vetoed, would also repeal federal funding for Medicaid expansion, which was estimated to have helped cover 11 million adults across the country in 2015. Ten Republican governors have taken advantage of the expansion, which was so successful in some places like Kentucky that, even though Gov. Matt Bevin (R) campaigned on scrapping the ACA, he simply made some tweaks to the program once he took office.

The Congressional repeal plan from 2015 would also repeal tax increases that were part of the ACA, likely shifting the burden for paying for health care from the federal government to individual states.

“Without that money, there is no way states could keep covering the 20 million people who have been covered under Obamacare,” Larry Levitt, vice president at the Kaiser Family Foundation, told TPM.

“It is looking like pressure is going to shifted back to the states but potentially without the financial resources to really make it work,” he added.

On Tuesday, Montana’s Republican House speaker, Austin Knudsen, warned that repeal could make it harder for Montana, which only voted to expand Medicaid in 2015, to pay for the program. He said that the state either was going to have to try to come up with some kind of solution, or else hope that Congress comes up with a fix itself.

“You’re going to tell me that we’re going to put 100,000 people on the Medicaid rolls and then when the federal government takes the money away we’re just going to jerk the rug out from under them? I don’t see that as being a realistic answer,” Knudsen told the Billings Gazette. “The state of Montana is going to have to look at trying to help keep those people covered. Whether I like the bill or not, it passed. It was signed into law. We covered a whole bunch more people.”

Red states across the country may face the harshest outcome if Obamacare is repealed early next year. The Los Angeles Times noted earlier this month that four of the five states whose residents receive the most in subsidies to help them buy insurance have Republican-controlled congressional delegations: Florida, Texas, North Carolina and Georgia. The 2015 Congressional repeal bill, however, would scrap the very same subsidies that help low-income people afford insurance.

A report from the Wall Street Journal also noted that the highest drops in the uninsured rate came in counties that Trump carried, where unemployment is higher and median incomes are lower than the national average. That suggests that when Obamacare is repealed, the very voters who supported Trump will likely suffer the most.

Yet it’s not state-level Republicans railing the hardest against repeal—it is, of course, the Democrats.

Last week the Democratic Governor’s Association sent a letter to Senate Majority Leader Mitch McConnell (R-KY) and House Speaker Paul Ryan (R-WI) arguing that repealing the ACA would result in states being saddled with an additional $69 billion in uncompensated health care costs for residents and could result in millions losing their insurance.

“Repeal would throw millions of our residents off their health coverage, shift enormous costs to state governments – blowing a hole in state budgets – and cause economic uncertainty for our states’ businesses, hospitals, and patients. This plan appears to be nothing more than a Washington, D.C. bait-and-switch that puts an untenable burden on the states,” read the letter, which was signed by Connecticut Gov. Dan Malloy, New York Gov. Andrew Cuomo and Washington Gov. Jay Inslee.

In Montana, Democratic Gov. Steve Bullock sent his own letter to Republican leaders in Congress urging them not to repeal ACA unless they have a replacement bill ready to go.

“Congress should not rip healthcare away from tens of thousands of Montanans and millions of Americans without first presenting a real and viable alternative that protects patients and provides a foundation for states, healthcare providers, and insurers to responsibly plan for the future,” Bullock wrote, according to a report from the Flathead Beacon.

In New Mexico, the state health care exchange had even drafted an unofficial letter from its Republican governor, Suzana Martinez, warning against Obamacare repeal. It turned out that the governor’s office never even saw the letter and had never signed off on the opinions contained in it. The bizarre episode laid bare the tension that exists as Republican leaders prepare to finally make good on a campaign promise that may adversely affect their state.

“Repeal may be attractive to Republican candidates, but when the reality sinks in about who is going to win and lose, it becomes a much harder proposition,” Levitt said.