With House Republicans poised to vote Thursday to dismantle the Affordable Care Act by replacing it with a pared-down health plan, a new California analysis reveals that the substitute would severely impact the state’s ability to pay for health care for its poorest residents.

The study released Wednesday by the Department of Health Care Services and Department of Finance shows that California would lose almost $6 billion in federal Medicaid funding in 2020 — a figure that would increase to $24.3 billion annually by 2027 if the GOP plan is passed by Congress and signed by President Donald Trump.

Along the way, the analysis said, the GOP’s health care law would also eliminate $400 million annually, starting in 2020, for the In-Home Supportive Services program, which helps keep nearly half a million of the state’s disabled and most frail seniors in their homes, sending them instead into much more expensive skilled-nursing settings. And it would cap the amount of money the state pays per person for Medicaid, the nation’s health care program for the poor, which is called Medi-Cal in California.

The enormity of the loss facing California may have been among the reasons Gov. Jerry Brown, on his first trip to Washington since Trump took office, ripped into the Republican plan Wednesday, saying it was “written by people who don’t know what the hell they’re talking about.”

Brown urged Trump to open his eyes to the “disease, death and suffering” the plan would bring to Americans.

“I came from California to tell the truth about this fake health care bill,” Brown said Wednesday at a rally on the Capitol steps, a day before the seventh anniversary of the Affordable Care Act’s signing by former President Barack Obama.

“This is not about health care reform. This is about disease, death and suffering,” Brown said. “Mr. Trump, come down from Trump Tower, walk among the people and see the damage that this latest exercise in raw political power will wreak on the women, the men and children of this country.”

The House is set to vote Thursday on the American Health Care Act, despite key concerns from several GOP factions that the proposal either goes too far — or not far enough — to replace parts of the current health care law, better known as Obamacare.

House Majority Leader Kevin McCarthy tweeted late Wednesday afternoon: “Seven years of #Obamacare is enough. Americans deserve a superior, patient-centered health system.’’

Each of the 14 California Republican House members has tens of thousands of Medi-Cal enrollees living inside their districts. Asked to comment on the California analysis in the face of their upcoming votes, Republican Congressmen Tom McClintock, Jeff Denham, David Valadao, Ed Royce and McCarthy did not respond Wednesday to emails and phone calls from the Bay Area News Group.

About a third of Californians are now enrolled in Medicaid. And nearly 4 million of roughly 14 million current enrollees have signed up for the program through a special provision of the Affordable Care Act that allows adults without dependent children to sign up for Medi-Cal.

State officials are particularly concerned because the federal government pays for almost all of the costs for the expanded Medi-Cal population, as opposed to only 50 percent of the cost for traditional Medi-Cal enrollees.

The Medi-Cal expansion — coupled with the Obamacare subsidies for Californians who buy insurance in the individual market — has helped reduce the state’s uninsured rate from 17 percent in 2013 to about 7 percent in 2016, according to the UC Berkeley Labor Center for Education and Research.

The analysis did not address the fiscal impact of the GOP health plan on the subsidies provided to more than 1 million Californians who buy through Covered California, the state-run health insurance exchange established under the Affordable Care Act.

All Medicaid enrollees must re-enroll annually, but under the GOP plan, those beneficiaries who signed up through the Obamacare Medicaid expansion would have to reenroll every six months to remain eligible for coverage. That would create an additional barrier that would “more than likely result in individuals not continuing with coverage,” Jennifer Kent, director of the Department of Health Care Services, said during a teleconference with reporters on Wednesday.

Under that assumption, state officials said, by 2027 nearly all of the several million enrolled in expanded Medicaid will not be eligible for enhanced federal funding because the new rules will cause chaos and lead people to drop off the expanded Medicaid rolls.

If the expansion Medi-Cal enrollees have a break in coverage for one month, they will all come back onto traditional Medicaid rolls, which means the federal government would be paying only half of the costs rather than 90 percent.

“It’s really devastating,” said Mari Cantwell, state Medicaid director with the California Department of Health Care Services, who co-wrote the analysis. “It raises some serious questions about whether we can continue to operate the program the way we do today.”

Although the analysis didn’t explain how the state would deal with the federal cuts, Cantwell told reporters it would have to look at changes to eligibility, benefits or provider rates – or all three.

Staff writer Katy Murphy and Kaiser Health News, an editorially independent program of the Kaiser Family Foundation, contributed to this story.

BY THE NUMBERS

14 million: Number of Californians now on Medi-Cal, the state’s health program for the poor

4 million: Number on “expanded Medi-Cal,” a provision under the Affordable Care Act that allowed adults without dependent children to enroll

$24.3 billion: Amount the Medi-Cal program would lose annually in 2027 under the GOP’s health care plan

$400 million: Amount California would lose annually beginning in 2020 for its In-Home Supportive Services program, which keeps the disabled and seniors in their homes rather than institutions

Sources: California Department of Finance, California Department of Health Care Services