One of the last holdouts among prominent Republican governors, New Jersey Gov. Chris Christie, put his state among a growing number that will defer to the federal government to run the health insurance marketplaces that are a key provision of the Patient Protection and Affordable Care Act.

The picture of which states would participate in providing tightly regulated individual and small-group coverage through the exchanges beginning in 2014 has rapidly clarified since the Nov. 6 election.

Under a Dec. 14 deadline to notify the Obama administration of plans to establish a state-based exchange, 21 states have indicated they will not form their own exchange. In states that decline, HHS will operate an insurance marketplace on its own or in partnership with state officials.

Like many of his peers, Christie complained that HHS has failed to provide states enough guidance to allow them to responsibly carry out the provision. "We will comply with the Affordable Care Act, but only in the most efficient and cost-effective way for New Jersey taxpayers," Christie said in a news release announcing the decision to veto legislation that would have started establishing a state-based exchange. "I will not ask New Jerseyans to commit today to a state-based exchange when the federal government cannot tell us what it will cost, how that cost compares to other options and how much control they will give the states over this option that comes at the cost of our state's taxpayers."

U.S. Rep. Frank Pallone Jr. (D-N.J.) issued a statement saying he was "deeply disappointed" in Christie's move because the Affordable Care Act intended for states to tailor exchanges to their own markets and communities.

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Another high-profile Republican opponent of the law, Arizona Gov. Jan Brewer, said on Nov. 28 that her state will not operate an exchange. Florida Gov. Rick Scott, who softened his resistance to complying with the Affordable Care Act after President Barack Obama was re-elected, has yet to reveal what course his state will take with its exchange.

Twenty of the states that have reached the same conclusion as Christie are led by Republican governors. In Missouri, where the governor is Democrat Jay Nixon, voters approved a ballot question prohibiting the governor from establishing an exchange by executive order.

In Michigan, it was the state's Republican governor who had been pushing for a state exchange. Late last month, though, a legislative committee blocked an exchange measure backed by Gov. Rick Snyder.

Eighteen states and Washington, D.C., intend to establish their own exchanges. Four states have indicated they will operate exchanges in partnership with federal officials in order to be ready to begin providing coverage under the reform law in 2014. About 25 million Americans are expected by 2022 to be covered under plans purchased through the exchanges, according to a July estimate from the Congressional Budget Office (PDF).'

Gregg Blesch is a reporter for Modern Healthcare, a sister publication of Business Insurance.