The Republican governor of Idaho gave advocates of expanding Medicaid a significant lift Tuesday, coming out in favor of the Obamacare policy just a week before voters in the state decide on its fate.

The question of whether to grow the low-income health-care program to cover more people is on ballots in three deep-red states — Idaho, Utah and Nebraska — where conservative legislatures didn’t choose expansion.

Outgoing Gov. C.L. “Butch” Otter, a conservative with an independent streak, announced his support and cut an ad for Idahoans for Healthcare, an organization advocating for expansion.

“We cannot continue to let hardworking Idahoans go without healthcare. I’m proud that the citizens of Idaho have come up with a solution to solve this long-standing problem,” Otter said in a release.

The ballot measure, Proposition 2, would cover up to 62,000 people and bring up to $400 million from federal coffers to the state. Otter also said it would keep rural hospitals and clinics open.

“I strongly support expanding healthcare to folks who need it. It’s good sense and it’s the right thing to do,” Otter said in the statement.

Medicaid expansion was a cornerstone of the Affordable Care Act’s goal to get more Americans health coverage. Initially it would have automatically kicked in across the country, with the federal government paying 100 percent of the costs before tapering down its share to 90 percent after a few years. But the Supreme Court ruled that individual states could decide whether to expand the program.

Currently, 33 states and the District of Columbia have expanded to cover individuals who fall into what’s known as the “Medicaid gap,” or people who earn at 100 percent to 138 percent of the poverty level. Those people struggle to buy health insurance on their own even with the assistance of Obamacare subsidies.

While the conservative politicians in Idaho, Utah and Nebraska have rejected expansion, arguing it ultimately will be too costly for the state, the idea has found support among some voters in those states, which each overwhelmingly elected President Trump.

Jonathan Schleifer, executive director of the Fairness Project, a national organization that helps bolster ballot initiatives, said the campaign has been successful because it was never billed as a partisan issue.

“We can make a huge difference by taking partisan labels off of good ideas,” he said.

Emily Strizich, a grass-roots activist with Reclaim Idaho, which is supporting the measure, said she has approached homes with “Make America Great Again” signs and found people agreeing with the measure on the other side of the doors. She said that last week she was out registering voters when a man with an NRA hat approached and told her, “It’s such a shame we’re sending money out of state, and our neighbors are going without support.”

“More than anything, people are putting their neighbors ahead of ideology,” she said.

The Republican gubernatorial candidate in Idaho, Lt. Gov. Brad Little, said he would support the will of the people if they vote to expand Medicaid. Democratic gubernatorial candidate Paulette Jordan supports the ballot measure.

Nebraska Gov. Pete Ricketts (R), who is running for reelection, has actively campaigned against the ballot initiative but is unlikely to block it if it passes.

Utah Gov. Gary R. Herbert (R), who supports a more limited Medicaid expansion, has not actively opposed the initiative.

Raymond P. Ward, a Utah GOP state legislator and family doctor, supports a more-limited Medicaid expansion but says he’s happy to see the Medicaid ballot initiative approved.

“I support it over doing nothing. I think we have to move forward and get that coverage to people,” he said.

Ward said he’s alone among most of his Republican colleagues who worry about future costs to the state if the program becomes too big or if the federal government stops paying its share.

Heather Williamson, of the Utah chapter director of Americans for Prosperity, which is actively opposing expansion, warned of the costs.

“As enrollment exceeds estimates, as it has in other states, Utah taxpayers would be forced to foot the bill,” she said.

Still, despite all three states being overwhelmingly Republican, the limited polling on the issue in Idaho and Utah have shown a majority of voters in both states support expansion.

“When you’re looking at states like Utah, Idaho and Nebraska there’s not that many Democrats there,” Schleifer said. “So even if every Democrat was on Medicaid, there’d still be a lot of Republicans on Medicaid — this issue is personal.”

If the ballot initiative is successful, Schleifer said his organization already is looking ahead to 2020 and has identified Florida, Mississippi, Missouri, Oklahoma, South Dakota and Wyoming as states to get Medicaid expansion on the ballot.

Paulina Firozi contributed to this report.