Senate leaders are taking the proposal seriously, as it offers something for conservative and moderate lawmakers, at least on paper. And, according to a Fox News interview with Marc Short, the White House director of legislative affairs, the Congressional Budget Office is evaluating the plan this week.

There is no public legislative language yet, but here’s how Mr. Cruz’s plan appears to work, based on his handout and statements: Any company that wanted to sell health insurance would be required to offer one plan that adhered to all the Obamacare rules, including its requirement that every customer be charged the same price. People would be eligible for government subsidies to help buy such plans, up to a certain level of income. But the companies would also be free to offer any other type of insurance they wanted, freed from Obamacare’s rules.

People who bought the Obamacare-compliant plans would be eligible for subsidies that limit their cost, as long as their income was less than about $42,000 per year for a single person. And those who earn more — or wish to buy skimpier, cheaper plans without all the rules — may also get a discount on those premiums, in the form of pretax health savings accounts, which the legislation would let them use to buy insurance.

As Mr. Cruz told Dylan Scott of Vox.com, “You would likely see some market segmentation,” meaning that healthy and sick customers would probably pick different kinds of insurance. Healthier, wealthier people would tend to gravitate toward the skimpy plans. Sicker people would opt for the compliant plans, which cover more benefits. Even though the compliant plans wouldn’t technically be more expensive for the sick, those choices would mean that mostly sick people would buy them, and the prices could get extremely high.

“There have been Nobel Prizes in economics awarded for the finding that when you allow an insurance market to segment like that, you end up with basically an unstable market,” said John Graves, an assistant professor of health policy at Vanderbilt University. Mr. Graves said that the government subsidies would blunt the financial impact for people below the income threshold, but the government would get stuck paying for most of the extremely high premiums.