President Obama in a speech in Boston on Wednesday accused Republicans of being “grossly misleading” about Americans being dropped from their health insurance plans because of Obamacare, the latest controversy surrounding the president's signature domestic achievement.

In Boston, Obama touted Massachusetts' health reforms as a model for what Americans could eventually expect from his own law, which has been plagued by the rocky rollout of

The White House has also been on the defensive about the president's repeated claim that all Americans could keep their health plans if they liked them. It was revealed this week that 14 million Americans on the individual insurance market though could lose their current plans and be forced to sign up for Obamacare exchanges because their coverage doesn't meet the law's standards.

Obama urged those being kicked off their old plans to give the new health law a chance.

"So if you're getting one of these letters, just shop around in the new marketplace,” Obama said from Faneuil Hall, where then-Massachusetts Gov. Mitt Romney signed his state's health law in 2006. “That's what it's for."

Obama and his surrogates argue that his earlier statements were accurate and that the public will keep their health plans provided the policy doesn't change. Additionally, they say those being dropped from their coverage plans will receive better insurance options through Obamacare. Republicans, though, have roundly rejected that claim and suggested the president misled the public about the effects of his law.

In his address, Obama urged patience during the rollout of his health reforms and drew parallels between his plan and Massachusetts’ so-called “Romneycare.” Administration officials say Obamacare will experience many of the same start-up problems and low enrollment numbers but that like Romneycare, the public will eventually appreciate the reforms.

Still, the president told the Massachusetts crowd he was “not happy” with the poor performance of the federal website registering consumers for new insurance exchanges.

"The website is too slow, too many people have gotten stuck and I'm not happy about it,” he insisted.

"I take full responsibility for making sure it works ASAP,” he added.

For Obama, it was a dramatic change of tone on Romney, his one-time presidential rival.

The president said that Romney had done the “right thing on health care” and that if Republicans worked with him the way the former Massachusetts governor had with Democrats, Obamacare would be easier to implement.

However, Romney was not invited to the event. And the 2012 Republican presidential nominee ripped the president for drawing parallels between Obamacare and the Massachusetts law.

“Had President Obama actually learned the lessons of Massachusetts health care, millions of Americans would not lose the insurance they were promised they could keep, millions more would not see their premiums skyrocket and the installation of the program would not have been a frustrating embarrassment,” Romney said in a Facebook post Wednesday.

The president's remarks came after Health and Human Services Secretary Kathleen Sebelius testified on Capitol Hill about the woes of Sebelius said that she, not the president, should be blamed for the problems — but provided few new details about what went wrong or how the technical issues would be fixed.