Kathleen Sebelius spent six years as the Democratic governor of red state Kansas, facing a wave of Republican opposition determined to thwart her at every turn.

Often underestimated, Sebelius would wait until the end of the legislative year and pressure centrist Republicans to make last-minute compromises.

“She had a fair amount of leverage because she was very patient and waited them out,” said Burdett Loomis, chairman of the University of Kansas political science department, who spent a year working for Sebelius as her director of administrative communications.

Now, as Health and Human Services secretary, Sebelius faces her biggest test of wills to date -- selling President Obama's signature health care overhaul to a skeptical public. This time there's no time to wait.

Starting Oct. 1, federal and state governments will begin enrolling individuals in subsidized health insurance exchanges. The insurance plans kick in on Jan. 1, 2014, alongside a slew of new health care mandates.

Insurers will be banned from denying coverage to individuals with preexisting conditions, Americans without insurance will be required to purchase a plan or face a penalty, and millions of low-income individuals will be added to state Medicaid rolls.

Sebelius, 65, is furiously crisscrossing the country to promote Obamacare, educate the public and work with recalcitrant governors, even as both supporters and critics wage high-profile campaigns to sway opinion.

Democrats say Sebelius’ experience as a governor and state insurance commissioner make her especially well-suited to implement the most significant changes to the health care system in decades. And supporters praise her for staying on in Obama’s second term to oversee the changes.

“She been through all the legislative fights and has a practical understanding of what this law means - how it will impact state governments and families at a micro-level,” said Rep. Robert Andrews, D-N.J., ranking member of a subcommittee on health and employment.

“She is mission driven,” said Ron Pollack, executive director of Families USA, a nonprofit devoted to expanding health care for Americans, and chairman of the board for Enroll America, a group helping enroll consumers in Obamacare. Pollack worked with Sebelius in the 1990s on a task force commissioned by President Clinton to write a patients' bill of rights.

Sebelius, though, has her work cut out for her — a reality she acknowledges.

“The politics has been relentless and that continues,” she said in an address at the Harvard School of Public Health.

Obamacare was signed into law in 2010, but partisan warfare over it remains intense. House Republicans have voted to repeal the law 40 times, and many conservative lawmakers are threatening to shut down the government if the bill isn't defunded. But with Obama in the White House and Democrats controlling the Senate, Sebelius is staying focused on putting it into effect.

Republicans charge that Obamacare will introduce a huge bureaucracy rife with fraud and abuse, undermine the quality of medical care and crush an already fragile economic recovery with costly new burdens on employers and consumers.

Democrats counter that Republicans are defending a broken system in which Americans pay far more for health care than any other country yet still suffer the prospect of debt if they experience a catastrophic illness or have a pre-existing condition.

Recent polls show the public is more confused than ever about the law, despite the administration’s promotional campaign, raising fears among Democrats that a botched rollout could hurt them in the 2014 midterms and beyond. Sebelius must also watch her left flank because labor unions, normally staunch Obama supporters, also oppose key elements of the law.

“This began as something that the president and the Democrats were on the winning side of and they ended up upside down on it,” said Chris Lehane, a Democratic strategist. “Now you have to put the other guys on defense – to show that they are supporting a system that has failed most Americans.”

Retiring Sen. Max Baucus, D-Mont., one of Obamacare’s chief authors, earlier this year famously predicted implementation will be a “train wreck.” Baucus recently backed away from those comments, but critics warn of trouble ahead.

“It's more like a series of train wrecks on the same track that will all pile up -- to a disastrous effect on the economy, employers and individual medical care -- right before the fall 2014 elections,” said Edmund Haislmaier, senior health policy fellow at the conservative Heritage Foundation, of the challenges facing Sebelius. “I'm not sure this is something Democrats have really thought through.”

Maintaining a consistent offense will be difficult for Sebelius with Republicans pouncing on every flawed or delayed provision.

The biggest setback so far came when the White House delayed a major provision that requires businesses with more than 50 employees to offer health insurance to full-time employees.

Obama downplayed the delay, saying it would give businesses more time to comply with the law. Republicans, though, seized on the change, demanding the administration also postpone the mandate forcing individuals to carry insurance or pay penalties.

Companies, including Trader Joe's and Walgreens, have also begun dumping some or all employees onto the exchanges, undermining Obama's promise that Americans who like their current employer-sponsored health plans could keep the policies they have.

Congress also balked at having to participate in Obamacare after a provision from Sen. Chuck Grassley, R-Iowa, required lawmakers and staff to enroll in the exchanges. After pressure from both parties, Obama ordered an exemption allowing congressional offices to continue to receive subsidies for insurance.

Administration officials insist that since Obamacare became law, health care costs have been slowing and premiums are increasing by the lowest rate in years. They blame Republicans for fanning fear and misinformation as the enrollment period begins.

“There have been very relentless efforts underway by opponents of the health law designed to undermine successful education efforts,” a White House official told the Washington Examiner.

The administration is ramping up their efforts in the last week before enrollment begins. Obama and former President Clinton discussed health reform at a Clinton Global Initiative event in New York on Tuesday. A White House official said the conversation would kick off an "aggressive six month public awareness effort."

Sebelius could have left government for a lucrative job in the private sector after Obama's first term. Instead, she remained a loyal lieutenant to the president and has dug in for the long fight.

Part of her motivation, supporters say, may have come from watching the political career of her father, John Gilligan, and recognizing the historic role she can play to bolster the core Democratic values her family embraced.

Gilligan, a free-wheeling Irish Catholic and Great Society Democrat who passed away late last month, represented the GOP stronghold of Cincinnati in Congress from 1965 to 1967 when Medicare and Medicaid were created. He was later elected governor of Ohio in 1970, but narrowly lost his re-election bid.

“Kathleen has probably proven herself a better politician than her father,” Loomis said. “John Gilligan had a little bit more of an Irish Catholic in him. If he had slightly smoother edges and was a less interesting character, he might have won more elections.”

By contrast, Sebelius is shrewd and disciplined, supporters say. After marrying the son of a conservative GOP congressman from Kansas in 1974, she moved to the state. She worked as the top lobbyist for the Kansas Trial Lawyers Association and had two sons, Ned and John, before running for elected office.

Sebelius rose quickly in Kansas politics, winning four terms as a state legislator, two as state insurance commissioner and two as governor.

When running for re-election in 2006, she co-opted some of her critics by choosing as her running mate a former Kansas Republican chairman who changed parties to join the ticket.

The bipartisan tactics she honed in Kansas, however, have failed to win over Republicans in Washington.

“She asked and the president asked Congress to give her an impossible job, and she's finding it impossible,” said Sen. Lamar Alexander, R-Tenn., ranking member on the Health, Education, Labor and Pensions Committee.

Alexander says Sebelius has pushed the limits of her authority, shuffling funds between government accounts after Republicans in Congress blocked efforts to provide additional money to help promote the new insurance options.

Republicans also question if Sebelius violated federal law by asking private companies to donate to Enroll America.

“I was very disappointed by that,” Alexander said. “Federal law doesn't permit a cabinet secretary to fundraise from a private entity or to use money appropriated for one purpose for another purpose.”

Sebelius defends her fundraising activities as outreach calls, saying she never explicitly asked for donations from the companies.

Democrats say Republicans are desperate to find fault anywhere they can to stall Obamacare, and they insist Sebelius is not discouraged by the negative press coverage.

“She and her staff are focused on what needs to be done in the day ahead as opposed to dealing with every little criticism that comes their way,” Pollack said. “This is a marathon, not a sprint.”