President Obama dismissed renewed criticism of his signature health-care law Sunday and disputed an assertion from a former adviser involved in its creation who said the administration had deceived lawmakers.

Jonathan Gruber, an economist, suggested last year that the legislation passed in part because of the “stupidity of the American voter” and a “lack of transparency” in its funding mechanisms.

“I just heard about this,” Obama said at a news conference after wrapping up two days of meetings with world leaders here at the Group of 20 summit. “. . . The fact that some adviser who never worked on our staff expressed an opinion that I completely disagree with, in terms of the voters, is no reflection on the actual process that was run.”

It was the first time Obama had weighed in on the comments, which became public after he left Washington for a week-long trip to Asia.

Gruber is an MIT economics professor and health-care policy expert who was a paid consultant for the Obama administration on the Affordable Care Act. His remarks were captured last year in a video that recently circulated widely on social media, and they have been seized upon by Republicans who want to dismantle the law. Conservatives in both chambers of Congress have said they might call on Gruber to testify on Capitol Hill, a process that would reopen the ugly political fight over a law that has enrolled millions of Americans in new health-care plans.

“We had a year-long debate,” Obama told reporters Sunday. “Go look back at your stories. One thing we can’t say is that we didn’t have a lengthy debate over health care in the United States. Every press outlet here should go back and pull up every clip and every story. It’s fair to say there is not a provision in the health-care law that was not extensively debated and was not fully transparent.”

Later Sunday, Health and Human Services Secretary Sylvia Mathews Burwell said 100,000 people submitted applications for coverage under the Affordable Care Act on Saturday, the first day of the law’s second enrollment period.

Speaking on NBC’s “Meet the Press,” Burwell said that more than 500,000 people were able to log on to the government’s Web site,, and that more than 1 million people have been “window shopping” for insurance options.

“I think the vast majority of people coming to the site were able to get on and do what they had to do,” she said.

The numbers and the apparent smoothness of the process are a stark contrast to last year’s rollout of the site, which was hobbled by technical difficulties.

Burwell also rejected the comments by Gruber, saying that she has “focused on transparency” as secretary. “The law is based on the issues of transparency and belief in the American people and choices in the marketplace,” she said.

In the news conference, which touched on several diverse topics, Obama also spoke for the first time about his face-to-face meetings with Russian President Vladi­mir Putin. The two leaders, whose relations have turned icy over Russian support for Ukrainian separatists, spoke informally several times at an economic forum in Beijing last week and at the G-20 summit in Brisbane.

Obama called the discussions “businesslike” and said he warned Putin that if he “continues down the path that he is on . . . the isolation that Russia is currently experiencing will continue.”

On the Islamic State, Obama reiterated that his thinking had not changed on his refusal to send ground troops to fight in the U.S.-led campaign against the militant group in Syria and Iraq. The president has authorized an increase in troops to act in support and advisory roles in the Middle East, but he said suggestions that his military advisers are requesting U.S. forces to fight on the front lines are wrong.

The president said that Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, has not recommended that he reverse his position. Rather, Obama said, Dempsey has envisioned hypothetical situations in which more direct action from the U.S. military would be required.

“Yes, there’s always a circumstance in which the United States needs to deploy U.S. ground troops,” Obama said. “If we discovered [the Islamic State] had gotten possession of a nuclear weapon, then yes, you could anticipate that not only Chairman Dempsey would recommend sending U.S. troops to get the weapons out of their hands, I would order it.”

The question, Obama continued, is: “What are those circumstances? I would not speculate on those.”

On immigration, the president acknowledged, when pressed by a reporter, that any changes to border-control laws that he makes through executive action could be overturned by the next president. Obama has vowed to act on his own after a comprehensive bill failed in Congress last summer, and he is weighing steps that could shield up to 5 million undocumented immigrants from deportation.

“The record will show I’ve actually taken fewer executive actions than my predecessor,” Obama said. “Nobody disputes that. What’s changed is the reaction of some of my friends in Congress about me exercising what are normal and frankly typical exercises in presidential authority. But you are right that the very nature of executive action means a future president could reverse that action. That’s always been true.”

The president also was asked about the potential for a government shutdown if his move to change immigration laws — action that Republicans fiercely oppose — sparks a political fight that results in conservatives refusing to pass a bill to fund the government beyond next month, when the current funding bill expires.

“I take Mitch McConnell at his word when he says the government will not shut down. No reason for it to shut down,” Obama said, referring to the Kentucky Republican who will become the Senate majority leader in January. “We’ve traveled that path before. It’s bad for the country. It’s bad for every elected official in Washington.”

Katie Zezima contributed to this report.