Obama acknowledged that there would be glitches in getting the exchanges up and running, and even as he was speaking, administration officials were quietly telling key interest groups to expect initial problems signing up for coverage online. Small businesses initially will not be able to enroll online and will have to sign up by paper, and the Spanish-language version of the HealthCare.gov website will be not be ready to handle enrollments for a few weeks. An estimated 10 million Latinos are eligible for coverage.

The ACA faces a crucial test starting Tuesday, when uninsured Americans begin enrolling in exchanges through which they will be able to buy individual health insurance. Computer glitches are slowing the rollout in areas such as Colorado, Oregon and Washington, D.C.

"The Republican Party has just spun itself up around this issue," he said. "And the fact is, the Republicans' biggest fear at this point is not that the Affordable Care Act will fail. What they're worried about is it's going to succeed."

With polls showing many Americans still skeptical of the Affordable Care Act (ACA), referred to by opponents as "Obamacare," the president went back to the basics of explaining how nearly 50 million uninsured Americans will be able to buy coverage in new government-run exchanges. At the same time, he mocked Republicans for trying to block its implementation. "The closer we get, the more desperate they get," Obama said.

With just five days to go before Americans can begin signing up for health care under his signature law, President Barack Obama on Thursday ridiculed Republican opponents for "crazy" doomsday predictions of the impact, and forecast that even those who didn't vote for him are going to enroll.

A greater concern

"Like any product launch, there are going to be some glitches," Obama told a crowd of about 1,800 people at Prince George's Community College in the Washington suburbs.

His greater concern is preventing the ACA from getting ensnared in efforts by Republicans in Congress to defund it in exchange for their agreement to approve spending measures to keep the government running and extend the U.S. borrowing limit.

The president faces two critical deadlines. The federal government will be forced to shut down on Tuesday if a spending measure is not approved, and it will run out of money to pay its bills on Oct. 17 unless the debt ceiling is raised.

Obama said Republicans fear that Americans will come to like the health care law, depicting their strategy as "'We've got to shut this thing down before people find out that they like it.'"

He won loud applause from a friendly audience when he vowed he wouldn't let Republicans block the law. "We are going to see it through. The Affordable Care Act is here," Obama said.

The six-month enrollment period for the exchanges starts Tuesday, with consumers in most of the country able to comparison-shop between plans online. The Obama administration needs millions of Americans -- especially young, healthy people -- to sign up in order to keep costs low for everyone.

The White House said Prince George's County, Md., where the president was speaking, has a high rate of uninsured people, with about 16 percent of residents under 65 without insurance. Obama's audience was full of the young people he is targeting for enrollment.

Obama didn't call out any of his Republican opponents by name, but he laughingly taunted some of their arguments. He mentioned House Speaker John Boehner's prediction, right before the bill was signed into law in March 2010, that "Armageddon" was impending. He quoted Louisiana Rep. John Fleming, who said earlier this month that "Obamacare is the most dangerous piece of legislation ever passed in Congress."

He cited Minnesota Rep. Michele Bachmann's appeal to colleagues on the House floor six months ago to "repeal this failure before it literally kills women, kills children, kills senior citizens."

And he quoted New Hampshire state Rep. Bill O'Brien's declaration in August that the ACA is "a law as destructive to personal and individual liberty as the Fugitive Slave Act of 1850." That was met by a chorus of gasps and boos from the largely black audience.

"Think about that. Affordable health care is worse than a law that lets slave owners get their runaway slaves back," Obama said. "I mean, these are quotes. I'm not making this stuff up.

"All this would be funny if it wasn't so crazy," he said.

Al Jazeera and wire services