Congressional Democrats conceded Tuesday that President Obama's “guarantee” that Americans could keep their existing health insurance plans under the Affordable Care Act was oversold.

Key Democrats declined to defend the broken promise made by the president during a contentious, yearlong debate that culminated with the March 2010 signing of the Affordable Care Act. But they said Obama's busted guarantee was the result of Obamacare regulations that require insurance companies to provide better, more comprehensive coverage.

Democratic Sen. Mark Begich said up to 3,000 Alaskans have lost their preferred insurance, but underscored that many who did had “junk policies.” But some Democrats expressed more pointed frustration and said the problem needs to be addressed. Louisiana Sen. Mary Landrieu, who like Begich is up for re-election in a Republican-leaning state, acknowledged that Obama’s claims were an important political sales pitch that she and other Democrats relied on to make their case for Obamacare.

“I said, and many people said, that this new law would allow people, if they wanted to keep what they had, to be able to do it. And, I think that we should live up to that promise. If we have to make some changes in order for that to happen, then we should,” Landrieu told the Washington Examiner. “The president said it many, many times. … I don’t think he intentionally oversold it, but if that’s not what’s happening then it needs to be fixed, because it was clearly a promise that he made.”

For several months, Americans who do not receive health insurance through their employer and who purchase coverage on the individual market have been receiving cancelations notices. Insurers have cited Obamacare regulations that set minimum standards for coverage and a range of newly mandated benefits as the culprit for the cancelations. Hundreds of thousands of individuals and their families have been affected.

Lawmakers familiar with the Affordable Care Act and its accompanying regulations were not surprised by the cancelations. They have long known that the sweeping changes Obamacare would impose on the health care system would almost certainly result in some Americans losing their existing plans, regardless of what the president promised.

NBC News reported that the Obama administration itself knew the president's guarantee could not be honored.

House Minority Whip Steny Hoyer, D-Md., said the White House and congressional Democrats told voters they could keep their plan to “allay fears” of those who had group policies or received coverage through their employers. The Maryland Democrat added that his party should have been “more precise” in explaining that individuals with insufficient coverage could lose their plans and access to their favored doctors.

Senate Majority Leader Harry Reid, D-Nev., told reporters that insurance companies are canceling policies because they do not adhere to the new “standards” of coverage and reliability mandated by Obamacare, including the new rule that bars insurers from rejecting applicants with pre-existing medical conditions. Reid described the cancelations as a negative aftershock of the law's otherwise positive effects. Sen. Max Baucus, D-Mont., suggested that no one should be surprised that this is happening.

“The law is very good, I’m glad we passed it,” said Baucus, the chairman of the Senate Finance Committee and a lead author of the Affordable Care Act. “There are glitches and problems with the rollout. I think the main focus should be, let’s fix it.”

Pressed on whether Democrats saw the cancellations coming and the veracity of Obama’s guarantee that Americans could keep their plans, Baucus would say only: “This is a massively complex undertaking and I think, let’s get — the main focus should be, let’s get it working.”

White House Press Secretary Jay Carney said Tuesday that Obamacare has fulfilled the president's promise for all Americans other than the 5 percent of the population that purchases coverage on the individual market -- about 14 million people. Carney implored the White House press corps to provide “context” to Obama's long-held claim, explaining that the president meant these Americans could keep their plan as long as it was still available.

But on Capitol Hill, Democrats are taking a different approach.

Senate Democrats are not distancing themselves from Obamacare. But they so far have not dismissed concerns raised by the cancelations, or tried to provide the context for Obama’s promise that Carney is demanding from the media. Some said they just want the problem fixed.

“I want to make it work, if it can,” said Sen. Joe Manchin, D-W.Va., who proposed a one-year delay of the individual mandate to purchase insurance. “Nobody should be forced to buy a product that’s inferior to what they’ve had or cost them more.”

White House Correspondent Brian Hughes and Congressional Correspondent Sean Lengell contributed to this report.