(CNN) – By accepting the provision included in President Barack Obama's health care law expanding federal Medicaid funding, Ohio Gov. John Kasich joined four fellow Republican governors in welcoming part of a program their party has campaigned vehemently against.
He also drew the ire of some Republican activists, who had viewed him as a model of small government conservatism and a potential candidate for the 2016 presidential nomination.
"Increasing the number of Ohioans on the rolls of Medicaid is not real health care reform and will ultimately trap Ohioans in a system that badly needs patient-centered reform," Seth Morgan, Ohio policy director of the conservative group Americans for Prosperity, explained in a statement. "We look forward to engaging with Ohio's policy makers to limit the reach of government into Ohioans' lives and pocketbooks."
Philip Klein, an editorial writer at the right-leaning Washington Examiner, called Kasich's decision "a huge victory for the White House that will provide cover for more Republican governors to do the same."
Kasich isn't the first Republican to sign on to the Obamacare provision – he joins Jan Brewer of Arizona, Brian Sandoval of Nevada, Susana Martinez of New Mexico, and Jack Dalrymple of North Dakota in endorsing the Medicaid expansion. In total, 19 states and the District of Columbia will accept the expanded federal funds.
Other Republican governors – including some who are considered potential 2016 presidential candidates – have rejected the measure, including Bobby Jindal in Louisiana and Rick Perry in Texas. Ten states in total have said no.
Governors Chris Christie of New Jersey and Bob McDonnell of Virginia, also potential presidential candidates, have yet to detail their plans on the Medicaid expansion.
Kasich announced the move Monday during a budget presentation, saying the rule expanding Medicaid coverage to adults with annual incomes at or below 133% of the federal poverty level would bring Ohio taxpayers' dollars back to the state.
"This makes great sense for the state of Ohio, and will allow us to deliver care using our dollars," he said, estimating that $13 billion would return to Ohio to allow unemployed or poor people to receive consistent health care.
The core of Obama's health care law, which was upheld last summer by the Supreme Court, is the individual mandate requiring citizens to obtain health insurance. But the court also upheld the provision expanding Medicaid coverage to include all adults with annual incomes at or below 133% of the federal poverty level, which is currently $14,404 for an individual.
The federal government will pick up the total cost of the expensive expansion for the first three years, after which the funding will phase down to 90%.
The expansion could reduce the number of uninsured adults with incomes under 133% of poverty by more than 11 million by 2019, according to a Kaiser Family Foundation estimate.
In their ruling, however, the court said that states can opt out of the Medicaid expansion program. The justices said the federal government can't penalize those states by withholding all Medicaid funding, but that they wouldn't receive the additional Medicaid money to cover newly eligible enrollees.
In his presentation Monday, Kasich made clear he wasn't a supporter of Obamacare and didn't believe in the individual mandate, but that by refusing the additional Medicaid dollars his state would set itself up for "financial chaos," since rural hospitals will soon no longer be reimbursed for treating uninsured patients.
He also cited the ability of the Medicaid expansion to strengthen the safety net for mentally ill people and addicts, saying it provided an "opportunity to rebuild that safety net so that we don't find mentally ill in jail because they receive no care."
"That's not acceptable in big state like Ohio," he said.
CNN's Tami Luhby contributed to this report.