The administration’s goal of having 10 million people enrolled by the end of next year, up from 9.1 million this year, is widely viewed as a low target that would represent a modest expansion of President Obama’s signature domestic program.

“It isn’t very much growth,” said Karen Pollitz, a former HHS official in the Obama administration who is now at the Kaiser Family Foundation.

While there is uncertainty about how the enrollment period will go, some fear that not enough healthy people will sign up to create a “risk pool” that balances the sick enrollees and prevents premiums from spiking.

“That would be a concern,” Pollitz said. “Sort of, how big of a risk pool do you need?”