(USA TODAY) -- President Obama denounced "irresponsible" Republican critics of hishealth care law Thursday, saying their threats could trigger a damaginggovernment shutdown and a U.S. credit default in the weeks ahead.

"They are now threatening steps that would hurt our entire economy," Obama said during a health care speech in Largo, Md.

Somemembers of the Republican-run House have said they will not approve anew spending plan - or an increase in the debt ceiling - unless thehealth care law is defunded.

Democrats who run the Senate said they will never allow such a tactic, and Obama said the same Thursday.

"That'snot going to happen as long as I'm president," Obama told supportersgathered at Prince George's Community College. "The Affordable Care Actis here to stay."

Obama spoke just five days before a pivotaldate: Tuesday, Oct. 1, sees the opening of new health care exchangesthat are key to financing the plan and fulfilling its goal of insuringnearly all Americans.

In his speech, Obama likened the new HealthInsurance Marketplaces to large group plans that will include companiescompeting for business, lowering prices while maintaining quality.

Tuesdayalso marks the first day of the next fiscal year. If the White Houseand congressional Republicans are unable to agree on a new spendingplan, parts of the government will shut down. Some GOP members said theywill not support any spending plan unless it makes changes to what theycall Obamacare.

Republican critics also say government subsidiesand regulations on insurance companies will force higher premiums formany Americans, and those costs will rise even more if not enough peoplesign up for the exchanges.

Citing polls that show publicopposition to the law, Senate Minority Leader Mitch McConnell, R-Ky.,said Obama is trying to sell his plan to "a skeptical public. It must befrustrating for him that folks seem to be tuning out all the happytalk."

Some Republicans also say they will not back an increase inthe $16.7 trillion debt ceiling unless the health care law is changed.On Thursday, House GOP leaders discussed an option to raise the debtceiling only if the health care plan is delayed for a year.

Obamasaid the debt ceiling gives the government authority to borrow money topay its bills; otherwise, the government will default. The TreasuryDepartment reports that it will be unable to repay debt starting Oct.17.

Congress is obligated to increase the debt ceiling withoutstrings because the nation's "full faith and credit" is at stake, and"you don't mess with that," Obama said. He again vowed he would notnegotiate on the issue.

Indefending his health care plan in general, Obama said there has been "alot of misinformation" that has generated "a lot of confusion." He saidthe law fixes a "broken health care system," and no longer allowsinsurance companies to discriminate against people with pre-existingconditions or illnesses.

Obama cited a recent report from theDepartment of Health and Human Services that said the average Americanwill have 53 different plans to choose from and 95% of uninsuredAmericans will see their premiums cost much less than expected.

Likeany new major program, "there are going to be some glitches as thisthing unfolds," Obama said, but those can be fixed along the way.

Obamasaid many Republicans are working to try and make the plan fail, butare worried that it will succeed and make them look bad politically.

Congress passed the law and the Supreme Court upheld it, he said, and he will not surrender it.

"We are going to see it through," Obama said. "The Affordable Care Act is here."

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