President Obama expressed regret Thursday for the "burden" he placed on fellow Democrats with the glitch-riddled rollout of his signature health care law, especially those facing re-election in the 2014 midterm elections.

"There is no doubt that our failure to roll out the [Affordable Care Act] smoothly has put a burden on Democrats, whether they're running or not, because they stood up and supported this effort through thick and thin," Obama said at a news conference. "I feel deeply responsible for making it harder for them, rather than easier for them, to continue to promote the core values that I think led them to support this thing in the first place."

Obama made the remarks while announcing an administrative fix for the health care law that would allow insurance companies to renew for a year the millions of existing health plans they canceled because those plans didn't meet Obamacare's stricter requirements. Obama had repeatedly promised that people who like their existing insurance plans would be allowed to keep him, but recently apologized for breaking that promise.

A provision had been added to the health care bill to preserve those existing plans, but Obama acknowledged Thursday that "it was insufficient."

The president insisted that his promise had been made in good faith, and pointed out that he was not the only Democrat who had believed Americans would be able to keep their plans.

"I think it's important for me to note that there are a whole bunch of folks up in Congress and others who made this statement, and they were entirely sincere about it," Obama said.

For some vulnerable Democratic incumbents running in 2014, the president's fix might not be sufficient. Sen. Mary Landrieu, D-La., who faces a difficult re-election bid, this week introduced legislation that would permanently preserve noncompliant health insurance plans, as opposed to the president's one-year extension.

One of Landrieu's Republican challengers, Rep. Bill Cassidy, charged Thursday that Obama and Democrats like Landrieu had misled Americans about Obamacare.

"It's pretty clear now, the president and Democratic senators lied to the American people," Cassidy said.

But during and immediately following the president's remarks, Democrats struck a publicly upbeat tone.

"For the record, I look forward to running on [Obamacare] next year," Michael Czin, a spokesperson for the Democratic National Committee, tweeted during the president's news conference.

Privately, Democrats called the president's plan a positive first step, but also said they expected to make additional changes to the law.

"You’ll also see Democrats go after Republicans who want to take us back to a time when patients could be denied coverage for pre-existing conditions, when women were forced to pay more for their care and when you could lose your coverage entirely if you got sick," a Democratic aide said.

Meanwhile, the president sought to downplay the political impact of the health care law on his presidency and his legacy.

"There are going to be ups and downs during the course of my presidency," he said.