President Obama offered a ringing defense of his signature health-care law Thursday amid what he called increasingly “irresponsible” Republican tactics to undermine it, ruling out changes as long as he is in office.

Traveling to Prince George’s Community College just outside the Capital Beltway, Obama made a moral argument, as well as an economic one, for legislation that will help define his domestic record for history. He said health insurance is now a “right” in the United States, not a benefit available only to those who can afford it.

“In the wealthiest nation on Earth, no one should go broke just because they get sick,” Obama told a friendly audience at the college in Largo. “In the United States, health care is not a privilege for the fortunate few, it is a right.”

Obama’s speech reviewed the history of legislation he signed more than three years ago, and offered a preview of the benefits to come when millions of people who previously could not afford health insurance begin buying plans offered within a federal exchange.

Enrollment, which he compared to “buying a TV on Amazon,” begins online next week.

Obama also delivered another warning to congressional Republicans that he will not accept delays to the program’s taxes, mandates and benefits, which GOP House members are seeking to make a condition of raising the debt ceiling next month. He said Republicans “have just spun themselves up over this issue.”

“The closer we’ve gotten to this date, the more irresponsible people opposed to this law have become,” Obama said, referring to the Oct. 1 start of enrollment.

Obama said he would not negotiate delays or other changes to the law as part of budget talks or the debt ceiling process, saying “the Affordable Care Act is here to stay.”

“No Congress before this one has ever, ever in history been irresponsible enough to threaten default,” Obama said, calling the tactic an effort to “blackmail a president for concessions.” “I will not negotiate on anything when it comes to the full faith and credit of the United States of America.”

Obama spoke without a suit jacket, his sleeves rolled up. And much of the talk featured Obama explaining in the detail of a consumer guide how to enroll in the new plans, which are prohibited from excluding those with pre-existing health conditions.

“It’s like booking a hotel or plane ticket,” he said of the plans, which take effect Jan. 1.

He implored Marylanders to enroll for coverage after the program takes effect next week.

“Tell your friends, tell your classmates,” Obama said at the end of his nearly hour-long speech. “We need you to spread the word. Go to the Web site. See what the questions are. See what the choices are. Make up your own mind.”

Obama made the case that the increased competition created by the new marketplace will drive down premiums for many others, part of his larger argument that a fully implemented health-care law will greatly benefit the U.S. economy.

“What is it that these Republicans are just so mad about?” he asked.

Answering his own question, Obama said the opposition is rooted in the wealthy having to pay higher premiums in some cases, the elimination of some tax breaks for deluxe plans and the requirement that businesses with more than 50 workers offer health insurance to employees or pay a penalty.

But, he said, “it is unfair for people to game the system and have the rest of us pay for it,” arguing that costs will be held down by new health insurance coverage that will help eliminate the need for many to use high-cost emergency rooms as primary care.

“Every time they have predicted something not working, it’s worked,” he said of predictions that the law cannot be implemented correctly. “Part of why I need your help to make this law work is because so many people out there are working to make it fail.”

He added later, “If it actually works, they will look pretty bad.”

U.S. Rep. Donna Edwards (D-Md.), one of a host of Maryland Democrats who also spoke at the event, said she has been uninsured and almost lost her home because of mounting hospital bills, and made a personal plea to young people to enroll. Also attending the event were Gov. Martin O’Malley, House Majority Leader Steny Hoyer and U.S. Sen. Ben Cardin.

Prince George’s County was considered an ideal location for Obama to tout his plan. A Democratic stronghold with a large middle-class population, Prince George’s also has a high number of residents who lack health insurance.

Amaris DeNeal, 21, of Forrestville, and Kimberly Thomas, 24, of Seabrook stood about 50 feet away from the president, who appeared on stage before a crowd of nearly 1,000 people packed into a gymnasium.

Neither of the full-time college students has insurance.

“I avoid doctor visits and emergency room visits at all costs,” DeNeal said. “This will at least give me some coverage to be seen.”

Thomas said she has accumulated numerous doctor bills since she was dropped from her parents’ insurance five years ago. She said she uses urgent care facilities in place of a primary care doctor.

“Anything Obama can do to help us to have affordable health care, I’m all for it,” said Thomas, who works part-time as a cashier at a store in a local mall.

After Obama’s speech, Thomas and DeNeal said they can’t wait to sign up and tell others about the plan.

“I just think it’s fantastic,” said Mildred Owens, who lives in Baltimore County and volunteers with a group that offers information about the new law. “I know people who don’t have insurance, and I have been sharing with them the same thing the president said today.”

Mark Hairston, 37, of Capitol Heights, who is unemployed and uninsured, said he hopes that Obama’s plan goes into effect next week and is not thwarted or delayed by Congress.

“It’s something that needs to move forward,” said Hairston, who worked in technical support for a cable company a year ago. “It would help me.”

Obama’s push comes amid lingering public confusion and skepticism over parts of the law, and many congressional Republicans have maintained their opposition after voting dozens of times to repeal or defund the legislation.

In a statement issued before Obama’s speech, Senate Minority Leader Mitch McConnell (R-Ky.) said that “the president will try yet again to sell his namesake health-care plan to a skeptical public.”

“It must be frustrating for him that folks seem to be tuning out all the happy talk,” McConnell said.