According to HHS, Americans living with pre-existing conditions such as heart disease, cancer, arthritis or high blood pressure are able to get the coverage they need under the full range of policies in the Patient Protection and Affordable Care Act enacted by 2014. Repealing the law, HHS said in a newly released report, would leave millions of Americans worried about whether they will have coverage when they need it.

HHS' calculation that as many as half of the nation's non-elderly adults, or roughly 129 million Americans younger than age 65, who would be unable to buy insurance or could see higher premiums in the individual insurance market is at the high end of the estimates the department has drafted. A more conservative estimate, based solely on individuals who have conditions that make them eligible for high-risk insurance pools, put the figure at 50 million, or 19% of non-elderly adults, according to the report.

The report emphasized that the reform law includes provisions that prohibit insurers, starting in 2014, from raising prices for those with pre-existing medical conditions or rejecting them entirely.

Michael Cannon, director of health policy studies at the Cato Institute, said the HHS estimate vastly overstates the problem. Cannon, during a Tuesday Capitol Hill discussion, referenced previous HHS surveys that have repeatedly found only 1% of Americans had ever been denied private insurance coverage because of pre-existing conditions.

House Republicans campaigned on a repeal of the Affordable Care Act. The House is scheduled to consider today a vote to scrap the far-reaching law, which was delayed following the shooting in Arizona that left six dead and injured Rep. Gabrielle Giffords (D-Ariz.) and others.