There has been no shortage of dire warnings about the mounting US national debt, but President Obama is now offering a different assessment: no big deal.

"We don't have an immediate crisis in terms of debt," President Obama said in an exclusive interview with George Stephanopoulos for "Good Morning America." "In fact, for the next 10 years, it's gonna be in a sustainable place."

It's an assessment that will throw cold water on the latest attempt to achieve a so-called grand bargain to reduce the deficit. After all, a grand bargain would require excruciatingly difficult decisions for both sides - for Republicans, it would mean raising taxes, and for Democrats, cutting future spending on cherished programs like Social Security and Medicare. If there is no crisis, why would either side do it?

So, what happens if this latest effort to reach a deficit agreement falls through? Once again, the president's answer was, essentially, no big deal.

"Ultimately, it may be that the differences are just too wide" to get a deal, President Obama said. "That won't create a crisis. It just means that we will have missed an opportunity."

The national debt clock is seen during Republican National Convention August 27, 2012. It has since grown by about a trillion dollars. (Stan Honda/AFP/Getty Images)

The president's reasoning is that the series of 11th hour agreements he has struck with Republicans over the last two years - to prevent a government shutdown, raise the debt ceiling and avoid the fiscal cliff - have resulted in enough deficit reduction to get the debt under control.

"I think what's important to recognize is that we've already cut $2.5- $2.7 trillion out of the deficit," he told Stephanopoulos. "If the sequester stays in, you've got over $3.5 trillion of deficit reduction already."

By that accounting, we have already achieved nearly all the $4 trillion the Bowles-Simpson debt commission called for back in 2010 - mission (almost) accomplished.

But there are two problems with that accounting:

First, the Congressional Budget Office projects a deficit of $845 billion - that's lower than the $1 trillion-plus deficits we've seen over the past four years and, as a percentage of the total economy, half the annual deficit of 2009. But, CBO also warns that the deficit is projected to continue rising once again after 2015, adding a total of $7 trillion to the national debt over the next 10 years.

Second, Erskine Bowles and Alan Simpson are now saying we are nowhere near accomplishing the amount of deficit reduction needed to put the government on sustainable path.

"They haven't done any of the tough stuff, any of the important stuff," Bowles told me last month. "They haven't reformed the tax code…they haven't done anything to slow the rate of health care, to the rate of growth of the economy, they haven't made Social Security sustainably solvent. There's about $2.4 trillion more of hard work we've gotta do."

Allan Simpson went further, calling the failure to control entitlement spending "madness."

"Ten thousand [Americans] a day are turning 65," Simpson told me. "This is madness. And life expectancy is 78.1, and in five years will be 80. Who is kidding who? This will eat a hole through America."

Urgent or not, the president seemed downright pessimistic about bridging the difference between Democrats and Republicans on how to further reduce the deficit.

"I am prepared to do some tough stuff. Neither side's gonna get 100 percent. That's what the American people are lookin' for. That's what's gonna be good for jobs. That's what's gonna be good for growth," President Obama said. "But ultimately, it may be that the differences are just too wide. It may be that ideologically, if their position is, 'We can't do any revenue,' or, 'We can only do revenue if we gut Medicare or gut Social Security or gut Medicaid' - if that's the position, then we're probably not gonna be able to get a deal."

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Transcript: President Obama Interviewed by George Stephanopoulos

ABC News