It was a question that seemed to be one of the most difficult for the current solicitor general, Donald Verrilli Jr., to answer persuasively, at least to the obvious satisfaction of the conservative justices: If the individual mandate for the purchase of health insurance was found constitutional, what would limit Congress from passing other laws requiring people to buy products from broccoli to cellphones?

Walter Dellinger, who served as solicitor general during the Clinton administration and supports the Affordable Care Act, seemed to have no problem with that one during an appearance on All Things Considered Tuesday with John Suthers, Colorado's attorney general, an opponent of the law whose state is part of a lawsuit against it.

When ATC co-host Robert Siegel put the bright-line question to Dellinger, the lawyer said:

"Sure. I don't think that's a hard question. Because the issue is whether the power to regulate commerce includes the power to require commerce. And the government's position is that you can require commerce on the part of people who are going to be inevitably engaged in the commerce for health care. When they do that they transfer the cost to others and it undermines the regulatory regime. That to me is a perfectly good limiting principle."

Perhaps the conservative justices would have been impressed by Dellinger's answer. Perhaps not. But he certainly delivered it with supreme confidence.

For his part, Suthers suggested to Robert there really could be no persuasive answer because the fundamental problem was that the federal government has no constitutional power to impose such mandates although states do.

Suthers: "This case has been about federalism from the beginning for the AGs. And the fact of the matter is, states are not burdened with enumerated powers that the federal government is. And under their police power, they probably can require people to buy insurance. Whether it's good public policy or not is another question."

As for Tuesday's oral arguments, Suthers was clearly encouraged by what he heard, while Dellinger seemed genuinely unsure which way the court will ultimately go. He agreed that his pro-ACA side got grilled more than the opposing side, especially by the court's conservatives.

Suthers: "I think myself and my attorney general colleagues are heartened. We filed this case two years ago last week. Took a lot of criticism. A lot of the legal community, constitutional law professors, said it was not a well-founded case. We were asking very fundamental questions. And today in the courtroom, we heard the justices zeroing in on those very questions."Dellinger: "I agree with John that more hostile questions were asked of the government overall than were asked of the challengers. But I came away from the argument not knowing what the outcome will be."And that's because I think that Chief Justice Roberts and Justice Kennedy, who sort of seemed to be in the balance of power, seemed genuinely troubled by aspects of each side's case. Obviously, they wanted to know what the government's limiting principle was. But I think they were concerned on the challengers' side that if you don't have this incentive for people to have insurance, and make it part of this insurance reform that uses the private market, is the only option going to be to have a single-payer, national, monolithic system?"Copyright 2016 NPR. To see more, visit http://www.npr.org/.