Health and Human Services Secretary Kathleen Sebelius already had a daunting job: playing the biggest cheerleader for Obamacare, a law that is unpopular with most Americans and that will define the president's legacy.

But now that the Obama administration has pushed back the requirement for employers to provide health coverage to their workers, the former centrist Kansas governor has turned into a political pi?ata for Republican lawmakers intent on killing Obama's signature legislative achievement.

"To a certain extent, [Sebelius] was shielded recently by the series of controversies enveloping the Obama administration," said a GOP House leadership aide. "That's not the case anymore. Quite frankly, I don't envy her job. She has to defend something that's indefensible. This is now our biggest target heading forward."

In Sebelius, the GOP sees a bureaucrat who knew the wheels were coming off Obamacare well before the administration announced the one-year delay of the employer mandate. Sebelius had said the government was prepared to implement the reforms while quietly seeking money from companies to promote the changes and reaching out to professional sports leagues to trumpet the overhaul.

After the recent capitulation by the White House, Sebelius now has to convince the public — particularly younger, healthier Americans who must buy into the program to keep it running — that the individual mandate should go ahead as planned.

"We strongly disagree with you that time will ever remedy these predictable consequences of the law," House Republican leaders wrote in a letter to Obama this week. "Many have predicted the problems that your administration now acknowledges, and each provision you delay continues to demonstrate that the entire law is unworkable."

Sebelius will make her sales pitch against the backdrop of the 2014 midterm elections, even as vulnerable Democrats are trying to distance themselves from the law back in their home states.

Obama tapped Sebelius, 65, for the Cabinet post after his top choice, former Sen. Tom Daschle, D-S.D., withdrew from consideration amid questions about unpaid taxes. Though some Republicans were open to the prospect of a moderate Midwestern governor, Sebelius has become a target in conservative circles — and not just because of Obamacare.

A federal judge last month ordered Sebelius to put a 10-year-old on an adult transplant list after she refused to move the cystic fibrosis victim ahead of other patients, despite doctors' fears that the girl would die without surgery. After the episode, some conservatives gave Sebelius a not-so-flattering nickname, calling her a "one-woman death panel."

Sebelius also drew the ire of conservatives for forcing religious organizations to provide their employees with health care coverage for contraception. Federal health officials also tried to restrict access to sales of the morning-after pill. But after a federal judge ruled that Plan B should be sold to girls of all ages, the Obama administration dropped its protest, angering conservatives.