According to experts, there are 3 different scenarios for the future of the USA.

In general it all depends on whether people will act reasonably or whether people will start to panic.

Scenario 1
~~~~~~~

The decline of the US dollar will slow down, Americans will start to spend less money. They will start saving money and consume less.
Imports will decrease and exports will start to rise because American goods and products will be cheaper then products from abroad and more competitive (cheaper then China?). This way the debts of the USA abroad will decrease and the decline in Dollar will finally be stopped. This would also mean China and the USA will "become friends" and there will the world economy will see a more balanced relationship between the USA and China

Scenario 2
~~~~~~~

The Subprime Crises will become worse...and not only affect mortgages but also private credits for consumer goods....this way all countries would loose trust in the US dollar and "sell" ther dollars in favour for more stable currencies such as the Euro or the British pound. This way the dollar would slide to an unrivalled all-time-low, lower then anyone would ever have imagined (China alone owns enough US dollars to play the role of the Federal Reserve Board, but in theory also with bad intentions!).
This of course would also lead to a crash on the stock market.
Even worse, other countries would also be badly affected - for example European countries could not export to the USA anymore and might suffer or even go bankrupt (Airbus etc..) and also badly effect the economy, too.

Ok, so both of these two scenarios assume considerate actions of all countries involved. But what if people start to panic ?

Scenario 3
~~~~~~~

What if all people who have heavily in invested all their money in the US dollar in the recent years, e.g. people and companies from China, Japan, Asia but also all oil-exporting countries such as Russia, start to panic because they are afraid of loosing almost all of their money?

This would lead to a horror-scenario: the US dollar crash.

This would of course to a world-wide economic crises....like the the 30s.

Of course a major role plays China. Communism will decide over the fate of Capitalism. Even a fraction of Chinese US dollar reserves would cause the US dollar to plummet.