TRENTON - Gov. Christie said Monday that more than a half-million New Jersey residents have gained health insurance as a result of his decision to expand Medicaid under the Affordable Care Act, even as he blasted President Obama's health-care law as an "incredible failure."

"Suggestions that if we did Medicaid expansion the right way, that we would further burden the state budget, were wrong then and are now proven wrong now," Christie, a Republican, said at a Statehouse news conference.

Conservatives criticized Christie when he agreed to expand the program in 2013 and during his unsuccessful presidential campaign this election cycle, arguing that he had embraced Obamacare and that states wouldn't be able to shoulder the costs.

Thirty-one states, including Pennsylvania, and the District of Columbia had expanded Medicaid as of July, according to the Kaiser Family Foundation, while 19 had not.

Since expansion took effect in January 2014, 567,000 New Jersey residents have enrolled in Medicaid, the government program for the poor and disabled, Christie said. That figure includes about 130,000 beneficiaries who would have been declared ineligible if the state hadn't expanded Medicaid.

Over the same period, he said, New Jersey's share of the cost of Medicaid has dropped from 45 percent in 2014 to 39 percent last year, with the federal government covering the remainder.

The average cost per beneficiary also is down, he said. Hospitals have reported fewer claims to state government for uncompensated care, creating savings in the budget.

Christie stood by his criticism of other parts of the health-care law, which created government marketplaces where individuals can purchase subsidized insurance plans. Christie has vetoed legislation that would have created a state-run exchange.

"The part of Obamacare that I strenuously object to is the part that's showing incredible failure: huge double-digit increases in premiums, insurers dropping out of Obamacare exchanges all across the country," he said.

The governor, who is a top adviser to GOP nominee Donald Trump, said he expected a Republican president would give states the choice to accept federal funding for Medicaid, as current law allows.