saying that it might be the global meltdown caused by the failure of financial system out side of the US. Which, in turn, will cause world financial system to fail. Even though I believe US financial system will be "fine" after all the efforts by US government, but other country's financial system's failure will cause US financial system to fail.

Right, if indeed there is a global meltdown and the meltdown will certainly not happen overnigh, then USD will be stronger (not devalue) in short term. But stocks will melt down and treasury will melt up...