IMNSHO -- the US dollar does not appear to be under any sort of massive coordinated attack, but rather is committing suicide.
The major US creditors such as the PRC, OPEC countries and Japan are losing massive amounts of purchasing power because of US dollar devaluation [QE], and will lose even more if the Dollar loses its reserve status.
To be sure there are most likely groups and individuals speculating against the US dollar and US denominated securities by shorting and/or derivatives, as Soros did against the UK Pound, but as the Godfather says, its nothing personal, its just business, and while they are planning to take advantage of the situation, they are not [directly] causing it to depreciate. Indeed the speculators have no need to act as Congress and the FRB are doing a very effective job.
One red flag [as in run, don't walk for the exits] will be a shift in OPEC oil pricing from US Dollars to Euros and/or Yuan or a big increase in international counter trade.
-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).