The Healthy Michigan plan paid for by the Affordable Care Act's Medicaid expansion likely wouldn't be sustainable under the expansion phase-out included in the repeal and replace proposal being pushed by House Republican leadership, Gov. Rick Snyder said Friday.

Snyder, who co-wrote a letter this week with Ohio Gov. John Kasich, Nevada Gov. Brian Sandoval and Arkansas Gov. Asa Hutchinson regarding the American Health Care Act, said he has serious concerns with the proposal on several fronts, including its plan to deal with the insurance marketplace and its potential to impact Michigan's traditional Medicaid program.

But the changes, if implemented, could have the biggest immediate impact on the Healthy Michigan program, which currently enrolls more than 650,000 Michigan residents. Snyder said the additional costs of paying for any new entries after 2020 under the American Health Care Act would cost the state $800 million more a year, "and that's not affordable."

"Essentially what you'd find is Healthy Michigan sort of winding down, where probably over 90 percent of the people on it would move out of the program within three years," Snyder said in an interview with MLive Friday. "That's a huge number, and it's difficult to see where that would come from" in the state budget.

Michigan Gov. Rick Snyder critical of GOP health care plan

That estimate is in line with a state Senate Fiscal Agency report released March 8, which found that if the Healthy Michigan statute was changed to continue the program if the American Health Care Act was implemented, the increased cost to the state would grow to $532.6 million in Fiscal Year 2020-21 and $738.9 million in Fiscal Year 2021-22.

Included in the letter to House and Senate leadership are suggestions Snyder and the other governors made to improve upon the American Health Care Act, including giving states more leeway to set up per capita systems, block grants or maintaining the current structure, depending on the needs of individual states.

Snyder said he believes Michigan's program so far has been successful, and said some reform options could "make Healthy Michigan even better than our traditional Medicaid program."

"We have people that are better off today - I clearly believe that's the case," Snyder said. "Instead of being in the emergency room, they're now getting primary care. If you think about it, that's a better answer for them in terms of their quality of life, and it's a better answer for society, because in the long term that should save us resources."

Although Snyder said he did not have time to discuss health care with the president when he visited the American Center for Mobility in Ypsilanti Wednesday, he said President Donald Trump, his administration and Republican members of Congress have been good about reaching out and hearing the concerns of governors.

He said he's hopeful some of the recommendations made by he and the other governors make it into the final proposal at the federal level: "I think there's good dialogue going on, but I would hope they could incorporate it if not in the House plan, than in the Senate plan," he said.

The GOP plan, dubbed the American Health Care Act, would phase out the Medicaid expansion and switch to a new funding Medicaid formula in which states get a set amount of dollars instead of the federal government guaranteeing to cover a certain percentage of Medicaid costs.

The plan also would change the current insurance subsidies based on income to one based on age, which means younger people would get more help to buy insurance but many older people would see higher out-of-pocket costs.

In addition, the GOP plan would eliminate the requirement for Americans to purchase insurance, although they would have to pay a 30 percent penalty on premiums for a year if they go more than two months without coverage.