Republican Nebraska Senator Ben Sasse said Monday he will block two of President Obama’s top nominees to the U.S. Department of Health and Human Services until there is a “complete and transparent accounting” of the financial crises that have led to the Obamacare co-op meltdown.

“I will act to block consideration and confirmation of every HHS nominee until families who lost their co-op insurance plans get straight answers,” Sasse said in a statement. Each of the 100 individual U.S. senators has the right under Senate rules to put a presidential nomination on hold for any length of time for any reason.

The Daily Caller News Foundation reported Monday that the Department of Health and Human Services’ Centers for Medicare and Medicaid Services, has a secret list of 11 Obamacare co-ops that face insolvency. The CMS manages Obamacare.

Obamacare co-ops have announced plans to close in the last two weeks in Colorado, Oregon, Tennessee, Kentucky, West Virginia and New York. In all, eight of 23 co-ops have gone under since the $2.4 billion Obamacare experiment in publicly funded health insurance co-ops began in 2012.

A ninth, in Vermont, was barred from operating at all by insurance regulators who concluded their financial plan was unrealistic.

Sasse, a Nebraska Republican, represents thousands of Nebraska co-op enrollees who lost their health insurance coverage last December in the collapse of the Co-Opportunity Health co-op. Co-Opportunity’s collapse cost U.S. taxpayers $178 million.

“Hundreds of thousands of enrollees lost their plans when co-ops in nine states collapsed and these victims deserve clear and honest answers from the bureaucrats who oversaw the mess. Until these families are given complete answers, the Senate should not confirm any HHS nominees,” Sasse said.

More than 120,000 customers in Iowa and Nebraska had to scramble to find new health insurance coverage after the Co-Opportunity debacle.

What was not publicly known during Co-Opportunity’s first year of operation was that the co-op was drowning in red ink.  It turned out the co-op offered attractively low premiums, but then had to pay out $1.40 in benefits for ever dollar it received in premiums.

Overall, the federal government so far has lost more than $900 million in failed Obamacare co-ops.

Prior to winning his Senate seat in 2014, Sasse served in HHS as an assistant secretary during the Bush administration.

To date, more than 415,000 customers from coast-to-coast have lost their health insurance coverage due to co-op failures.

Among the nominees subject to Sasse’s hold is Andy Slavitt, the acting administrator to the Centers for Medicare and Medicaid Services.

Slavitt faces a host of ethical and conflict of interest problems. Prior to joining CMS Slavitt was an executive at United Health Group, the nation’s largest commercial health insurer which derives at least a third of its income from CMS.

Last May, Sasse asked HHS Secretary Sylvia Burwell asking for the reasons why Co-Opportunity Health was awarded federal loans in the first place.

Stephen Ringlee, a Co-Opportunity founder, was inexperienced in health care and suffered a string of start-up failures prior to setting up the co-op.

On August 6, Sasse sent a second letter to Burwell with nine specific questions about the co-op program, telling her he was “disappointed” in her initial response. Burwell never responded to Sasse, according to his staff.

Sasse’s other hold is on Obama’s nomination of Karen DeSalvo as assistant secretary of health and human services.

Follow Richard on Twitter