(CNN) - President Barack Obama called on his fellow Democrats to "forcefully defend and be proud" of the fact that millions of people have signed up for health care insurance through the federal marketplaces, and faulted Republicans who are still angling to repeal the Affordable Care Act.
"I don't think we should apologize for it. I don't think we should be defensive about it. I think there is a strong, good, right story to tell," Obama said Thursday during a rare appearance at the daily White House news conference.
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Obama announced that the number of people who have signed up for private insurance through the marketplaces has grown to 8 million. About 35% of those people are under the age of 35, he added. That number is slightly less than the 40% that the White House and independent experts originally forecast for the system to work successfully, but it's higher than numbers released earlier this year.
Obama said the law is "now covering more people at less cost than most would have predicted just a few months ago" and criticized its opponents.
"I find it strange that the Republican position on this law is still stuck in the same place that it has always been. They still can't bring themselves to admit that the Affordable Care Act is working," the President said.
"They said nobody would sign up; they were wrong about that," he continued. "They said it would be unaffordable for the country; they were wrong about that.
The President said the political bickering will still likely continue through at least the November midterm elections, "because it seems as if this is the primary agenda item in the Republican political platform."
His comments marked a strong contrast to the tone he took last November as his administration was trying to smooth over the rocky rollout of the federal website, as well as a broken promise that anyone who liked their insurance would be able to keep it under the new law.
Vulnerable Democrats have since tried to place distance between themselves and the health care law, an outcome Obama somewhat anticipated last fall.
"There is no doubt that our failure to roll out the ACA 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," the President said at a press briefing.
The President added that he felt "deeply responsible for making it harder for them rather than easier for them."
But after the administration ended up exceeding its original goal of 7 million sign-ups by the end of March, the President and the White House have not been shy in celebrating a victory.
"This thing is working," Obama said Thursday.
"If Republicans want to spend all their time talking about repealing a law that's working, that's their business," he added.
He also chided states that have refused to accept Medicaid expansion, a provision in the health care law that would give states federal dollars to increase the amount of people who could qualify for the program. Nearly half the states-all with Republican governors-have declined to accept the program, while a few states are still considering it.
Obama argued governors and state legislatures have chosen not to expand Medicaid "for no other reason than political spite."
CNN's Dana Ford contributed to this report.