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Threat of debt default hangs over US

So far Wall Street has brushed off worries about the deadline to do a deal on America's borrowing limit.

But the pressure is mounting - the US dollar has weakened and the concern about the once unthinkable default is growing.

Analysts are starting to crunch the numbers for the US losing its triple-A credit rating.

JP Morgan estimates it could cost the government $100bn a year.

Caroline Hepker reports.

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