– Barack Obama won the presidency by exploiting a political environment that devoured George W. Bush in a second term plagued by sinking credibility, failed legislative battles, fractured world relations and revolts inside his own party.

Obama is now threatened by a similar toxic mix. The disastrous rollout of his health care law not only threatens the rest of his agenda but also raises questions about his competence in the same way that the Bush administration's botched response to Hurricane Katrina undermined any semblance of Republican efficiency.

But unlike Bush, who faced confrontational but occasionally cooperative Democrats, Obama is battling a Republican opposition that has refused to open the door to any legislative fixes to the health care law and has blocked him at virtually every turn.

A contrite-sounding Obama repeatedly blamed himself Thursday for the bungled health care rollout, which he acknowledged had thrust difficult burdens on his political allies and hurt Americans' trust in him.

The president did not admit to misleading people about whether they could keep their health insurance, but again expressed regret that his assurances turned out to be wrong.

Earning back the confidence of Americans, as he pledged to do, will require Obama to right more than just the health care law. At home, his immigration overhaul is headed for indefinite delay, and new budget and debt fights loom. Overseas, revelations of spying by the National Security Agency have infuriated U.S. allies, and negotiations over Iran's nuclear arsenal have set off bipartisan criticism.

For the first time in Obama's presidency, surveys suggest that his reserve of goodwill among the public is running dry. Two polls in recent weeks have reported that a majority of Americans no longer trust the president or believe that he is being honest with them.

The difficulties have put Obama on the defensive at exactly the moment he might have seized political advantage in a dysfunctional Washington. If not for the health care disaster, the two-week shutdown of the government last month would have been an opportunity for Obama to sharpen the contrast with Republicans.

Democratic lawmakers expressed growing frustration on Thursday with the opportunities the party has missed to hammer home the ideological differences between the two parties. The lawmakers say there is intensifying anxiety within the Democratic caucus that the poor execution of the health care law could bleed into their 2014 re-election campaigns.

Republicans readily made the Hurricane Katrina comparison.

"The echoes to the fall of 2005 are really eerie," said Peter Feaver, a top national security official in Bush's second term. "Katrina, which is shorthand for bungled administration policy, matches to the rollout of the website."

The president's top aides vehemently reject the comparison. They say Americans lost confidence in Bush because of his administration's ineptitude on Hurricane Katrina and its execution of the war in Iraq, while Obama is struggling to extend health care to millions of people who do not have it. Those are very different issues, they said.