PHOENIX — When Gov. Chris Christie  (R) said in February that New Jersey would expand Medicaid under the Affordable Care Act, he opened the door to health care coverage for 104,000 of the poorest Garden State residents, a move he said would save the state $227 million this year alone.

He also may have complicated his own hopes of making it through a competitive Republican presidential primary in 2016, when rivals will be looking for any, and every, opportunity to distinguish themselves from the rest of the crowded field.

Christie is one of just eight Republican governors to accept the expansion. He and Gov. John Kasich (R), of Ohio, are the only two who have both expanded Medicaid and who are said to harbor White House ambitions. Expanding Medicaid will make most adults who earn up to 138 percent of the federal poverty limit eligible for coverage. The federal government will cover 100 percent of the costs of the expansion for the first few years of the program, and 90 percent of the costs going forward.

Already, Christie’s rivals have cast his decision as an endorsement of Obamacare, a measure Republican primary voters almost universally loathe.

“On the case of the New Jersey governor, I think embracing Obamacare [and] expanding Medicaid in his state is very expensive and not fiscally conservative — and, really, many Republican governors who I would say are conservative did resist expanding and accepting Obamacare in their states,” Sen. Rand Paul (R-Ky.) said Tuesday on CNN. “That fact, I would say, would lead towards you making the conclusion that it’s not a very conservative proposal.”

Several strategists working for other potential White House candidates said the negative television advertisements virtually wrote themselves. Accepting expansion, they said, can be easily framed as an overt endorsement of the underlying bill.

“In the standard attack ad, the governor’s face will turn into President Obama’s, and the voiceover will say that a vote for the governor is a vote for Obamacare,” said John Pitney, a political scientist at Claremont McKenna College and a former top staffer at the Republican National Committee. “These spots will feature more morphing than a ‘Terminator’ movie.”

One strategist working for a potential 2016 candidate, who asked not to be named while discussing internal strategy so far in advance of the Republican primary, pointed to George Voinovich, the former Republican governor and senator from Ohio. Voinovich, then governor, was atop former Sen. Bob Dole’s list of potential vice presidential running mates in 1996 until a Wall Street Journal editorial pointed out his record of raising taxes and dubbed him “Rockefeller Voinovich.”

The strategist said after Kasich moved to expand Medicaid in his state, he crossed Kasich’s name off the list of his boss’s potential rivals.

Asked by a reporter at the Republican Governors Association’s annual meeting here whether having expanded Medicaid would make the road to the Republican nomination more difficult, Kasich said: “Is that how you’re going to make a decision?”

“Anybody who would be making the decision from that standpoint I wouldn’t want to be supporting for president,” Kasich said. “I think all things kind of fade over time.”

Most Republican governors tout the fact that they turned down Medicaid expansion, saying they don’t trust the federal government to keep its commitment to cover 90 percent of the costs in the future. But they are loathe to criticize their colleagues who came to different conclusions.

“I just came to the conclusion that expanding traditional Medicaid was not in the interest of Hoosiers’ health and it was not in the fiscal interest of the state of Indiana,” Gov. Mike Pence (R) said in an interview.  “That was a decision that every governor had to make based upon the unique circumstances in their own state.”

“I think it’s going to be an issue, certainly, that is talked about just like others. But it won’t be the sole issue,” said Nikki Haley, governor of South Carolina, home to the first-in-the-South presidential primary.

Christie will formally take the reins at the RGA after a governors-only meeting late Thursday. The new position will give Christie an opportunity the hobnob with high-dollar donors, and to travel around the country laying groundwork for a possible presidential bid; former Republican presidential candidates like Mitt Romney and Rick Perry have used the RGA as national springboards in the past.

Christie takes the reins from Louisiana Gov. Bobby Jindal, another Republican with national ambitions — and one of the majority of Republican governors who said no to a Medicaid expansion.

“I do think everybody should have health insurance,” Jindal said in an interview. “I just think ACA and Medicaid expansion were the wrong way to solve that problem.”

But even Jindal, a GOP star since he won the governorship in 2007, declined to draw an early contrast with Chrsitie.

“Every governor has to make the best decision for their state, so I’ve never second-guessed or criticized or questioned those governors who made a different decision than I did,” Jindal said. “Let’s stop thinking about 2016.”

Iowa Gov. Terry Branstad (R), who signed Medicaid expansion into law earlier this year and who has made no secret of the fact that he wants a governor to win his party’s presidential nomination, said voters in his first-in-the-nation caucus state would look beyond Medicaid expansion when evaluating candidates.

“I think people are going to look at the big picture,” Branstad said. “Medicaid is just one small issue.”

Dan Balz contributed to this story.