Arizona Gov. Jan Brewer gives a thumbs-up to hundreds of supporters as she touts her Medicaid expansion plan during a May 15 rally at the Arizona Capitol in Phoenix. (Ross D. Franklin/Associated Press)

Republican fissures over the expansion of Medicaid, a critical piece of the 2010 health-care law designed to provide coverage to millions of uninsured Americans, continue to deepen, with battles in Arizona and elsewhere showing just how bitter the divisions have become.

Despite expressing distaste for the new law, some GOP governors have endorsed an expansion of Medicaid, and three — Jan Brewer of Arizona, John Kasich of Ohio and Rick Snyder of Michigan — are trying to persuade their Republican-controlled legislatures to go along. The governors are unwilling to turn down Washington’s offer to spend millions, if not billions, in their states to add people to the state-federal program for the poor. But they face staunch opposition from many GOP legislators who oppose the health-care law and worry that their states will be stuck with the cost of adding Medicaid recipients.

In one of the most explosive of the internal Republican battles, Brewer, a firebrand tea party favorite who once wagged her finger at President Obama, has declared a “moratorium” on all other legislation until her Medicaid plan, which would add 300,000 Arizonans to the program, is approved. She has backed up her threat by vetoing five unrelated bills.

In Ohio and Michigan, the governors are pressing for last-minute compromises before their legislatures adjourn this summer. The Florida legislature, which has adjourned, rejected Republican Gov. Rick Scott’s plan to expand Medicaid.

These conflicts over the health-care law illustrate a larger divide within the Republican Party over an array of issues, including immigration and automatic budget cuts.

The Medicaid expansion is one of the two main ways the health-care law would provide coverage to the uninsured. The other is through health insurance exchanges, which will sell policies to individuals whose incomes are too high for Medicaid; many of those people will receive subsidies to buy the health plans.

Medicaid eligibility varies from state to state and depends on income and other factors. The health-care law, in an effort to make eligibility uniform, mandated that anyone earning up to 138 percent of the poverty level, or $15,856 in 2013 dollars, be eligible for the program. But last June, the Supreme Court, while upholding most of the health-care law, ruled that states could refuse to expand their Medicaid programs. That set the stage for bitter debates — ones ruled as much by ideology and politics as by financial realities — that have been occurring in state capitals nationwide.

Under the law, the federal government will pay 100 percent of the cost of newly eligible Medicaid recipients for the first three years, beginning in January. After that, the federal contribution will taper, leveling off at 90 percent for 2020 and beyond.

Twenty-three states and the District have agreed to the Medicaid expansion. Nineteen states have decided against the expansion and eight are debating it, according to Avalere Health, a consulting firm. States that decline to expand Medicaid now can still sign up in later years.

The debate over Medicaid has been emotional and vitriolic in many states. In Texas, Gov. Rick Perry (R) was heckled during a recent speech for opposing an expansion. In Montana, chaos erupted after a lawmaker accidentally voted against expanding the program, causing the measure to fail. Medicaid advocates in some states, frustrated by inaction from their elected leaders, are working to put the matter to voters in the form of ballot initiatives.

The hostility is evident in Arizona, where authorities are investigating a threatening phone call and e-mails directed at lawmakers who support expanding the program. Opponents of the expansion have condemned the alleged threats.

Brewer’s support for the expansion has stunned longtime backers, who have come to relish her gritty, confrontational persona. These supporters were gleeful last year when photos showed her defiantly pointing a finger at the president on a tarmac in Phoenix during what she later described as a tense conversation about her characterization of Obama in her memoir, “Scorpions for Breakfast.”

Now, her former fans label her a traitor and deride her Medicaid proposal as “Obrewercare.”

“It’s typical of these politicians,” said Dara Vanesian, chairman for the Navajo County Republican Committee. “This is not truly about the individual or rights or what’s best for Arizona. This is Brewer looking at dollars that are supposedly going to come from the federal government.”

Brewer may win, despite the opposition. Her measure has passed the Republican-controlled state Senate. There is stronger opposition in the House, which has a larger and more conservative Republican majority. State Rep. John Kavanagh (R), chairman of the House Appropriations Committee, said the committee plans to strip the Medicaid expansion from the budget.

He acknowledged that his members are feeling the heat after Brewer’s vetoes. Still, he added, conservative lawmakers would be hard-pressed to vote yes on the Medicaid expansion after years of railing against the health-care law and federal spending.

“For the last five years, almost every one of us Republicans have been bashing Obamacare and vilifying the federal government for irresponsible government spending,” Kavanagh said. “I have never seen a more toxic vote for Republicans than to vote yes on this expansion.”

Matthew Benson, a spokesman for Brewer, said the governor is confident that the Medicaid proposal will ultimately pass the House. Despite the vocal opposition from within her party, he said she has the support of many traditionally conservative groups, including 14 of the state’s 15 sheriffs and the Arizona Chamber of Commerce.

“We recognize that the ‘Obamacare’ title is what makes this controversial,” Benson said. “If it weren’t for that aspect of it, this plan would have gotten done months ago.”

Brewer, who joined the unsuccessful lawsuit last year to strike down the health-care law, has tried to walk a blurry line on the issue. She has maintained her opposition to the legislation and insisted that her Medicaid proposal is not the same as Obama’s.

Her office has argued that the Medicaid plan will spur growth by providing money to hospitals and pumping $2 billion into the Arizona economy. And she has said she will pull the plug if it appears that the federal government will not come through on its promise to fully or mostly fund the expansion.

“When I introduced my Medicaid restoration plan in January, I knew it wasn’t going to be easy,” Brewer said at a rally in Tucson. “I knew the road was going to be tough. And I knew there were going to be opponents. But let me tell you something else. I don’t think the opponents realize how hard we are going to fight.”

Arizona was the last state to join Medicaid, signing on in 1982, 17 years after the program was created. Today, it covers many childless adults who earn up to $11,490, the federal poverty level for that demographic and a more generous amount than most states.