There are two significant signs, one official, one anecdotal that are a true measure of the health of the U.S. economy.
The first is that incomes declined in the last quarter, in spite of all the glowing reports of GDP expansion. Where is all this supposed wealth going? In fact incomes in real terms have been stagnant since the 1970s in the U.S., and have now started an inexorable decline in purchasing power. Consumer credit has ballooned to compensate, but this obviously will create another imminent credit and banking crisis, as consumers as a whole will not be able to meet their obligations.
The anecdotal example is that of New Orleans after Katrina. No one could think that this devastation of a major American city would not have been met with an enormous public works response in the 1950's or 60's. The tepid response it did receive, which sees the the city hobbling along 3 years later, its residents scattered and many still living in trailers, at half its former size, is a direct result of the bankruptcy of American government. The original disaster was created by the crumbling infrastructure of America, which is receiving far less in investment than is needed even to maintain the status quo.
The two milestone events that signalled the end of American economic sovereignty and vitality occurred first in the 1970's when Republican Richard Nixon dismantled the Bretton Woods agreement, throwing its and the world's currencies to the 'mercy' of an international casino, run by speculators and hedge funds. The other was the implementation of NAFTA by Democrat Bill Clinton, which hopelessly compromised America's industrial integrity, betraying his own constituency. In fact the latter, was simply one event of a series of tariff dismantling agreements stretching back decades, under the aegis of GATT and the WTO.
America and the world is now run by faceless speculators and bureaucrats at the WTO, IMF and World Bank. All committed Free Trade zealots, who will use any measure of austerity and duress to induce small nations to capitulate the world investment and trading and organism.
It is corrupt, it is intolerably cruel, and it is coming home to roost in the First World.
The most pressing concern of world financial system stability has been the proliferation of exotic trading derivatives. Really gambling instruments for currencies that now account for many times the world's productive capacity to meet their nominal value. We have seen apparently healthy leveraged hedge funds disappear overnight on a misplaced bet.. Bear Stearns being the latest. The entire system is without integrity and will ultimately collapse, swept away, with devastating effects.
That is what the next President will have to deal with, a rising flood pushing at a decrepit tariff, monetary and regulatory levees systems, and frankly neither McCain or Obama have an inkling that there is even a problem.