"if you ask many opponents of this law what exactly they'd do differently, their answer seems to be, well, let's go back to the way things used to be," the president said.
"Just the other day, the Republican leader in the Senate [Sen. Mitch McConnell of Kentucky] was asked what benefits people without health care might see from this law, and he refused to answer even though there are dozens in this room and tens of thousands in his own state who are already on track to benefit from it. He just repeated 'repeal, repeal, repeal,' over and over and over again."
Obama added, "You can't just say the system was working with 41 million people who didn't have health insurance."
But, the president said, "Our poor execution in the first few months on the website clouded the millions of people who stood to benefit" from implementation of the Affordable Care Act.
"We need to make sure that folks refocus on what's at stake here," Obama said.
McConnell, in a statement issued Tuesday, said, "Another campaign-style even won't solve the myriad problems facing consumers under Obamacare."
"The American people have been learning about the impact Obamacare will have on individuals and families in the form of higher premiums, disrupted insurance and lost jobs — more broken promises from the administration," McConnell said.
"And they're becoming increasingly aware of the fact that Obamacare is broken beyond repair. The only fix is full repeal followed by step-by-step, patient-centered reforms that drive down costs and that Americans actually want."
But Dr. Sam Weir, a physician cited by Obama in his speech for his support of the Affordable Care Act, told CNBC.com that "many of my patients are looking forward to getting coverage."
"From where I sit, anything that expands coverage of people who have to make choices about what medicines to take because they can't afford them, or they end up in the emergency room because haven't gotten the preventative care they need, those are important steps in terms of health care policy," said Weir, medical director of family medicine at the University of North Carolina School of Medicine.
Weir had emailed the White House to voice support of the Affordable Care Act after checking out plan prices on HealthCare.gov for North Carolina residents, and being "just really struck by what a change this presents for the population that I take care of." He said about 11 percent of his facility's patients lack insurance now.
"My patients and patients all around the country are going to be able to get the services they need," Weir said.
Asked about Obamacare's many critics, Weir said, "I think that for some folks in the political arena, if the president said the sky was blue, they'd be opposed to that notion."
—By CNBC's Dan Mangan. Follow him on Twitter