Senator Richard Durbin of Illinois, the chamber’s second- ranking Democrat who was instrumental in pushing through the law, said there’s “legitimate concern” that care will remain unaffordable for some.

Lawmakers sought to “protect the poorest” yet weren’t able to offer as much help to others as they would have liked because of budgetary constraints, said Durbin. “We did all that we could do,” he said.

“If we find out that it doesn’t reach our goal then we’re going to have to sit down and work with it,” he said.

He said Republicans have “no response” to the question of how to expand coverage to the uninsured.

A November 2009 analysis by CBO of a draft of the program provides a rough indication of how quickly the subsidies will ramp down. It shows the government covering 77 percent of the premium costs for single persons earning about $20,600, 42 percent for those earning around $32,400 and 13 percent of the premium costs for those making about $44,200.

That means many with modest incomes will be responsible for covering the bulk of their premium costs. About 5 million people required to buy coverage won’t receive any help from the government because they earn too much, CBO projects.

Managing Expectations

“There may not be sufficient management of expectations,” said Lynn Quincy, a health-policy analyst at Consumers Union, a Yonkers, New York-based advocacy group. Lawmakers should have been telling the public the law promises “lower-cost” -- not “affordable” -- coverage, she said. “Everybody interprets ‘affordable’ differently -- it’s in the eye of the beholder.”

The Obama administration defended the law.

“Independent, nonpartisan experts have said the health- care law will help cover 30 million people who don’t have insurance today,” White House spokesman Nick Papas said in a statement. “The law takes substantial steps to control costs and will save money for millions of Americans.”