"Since becoming a free-floating currency, the US dollar while seeing a gradual decline in value against its main trading partners, has seen some very powerful multi-year price swings in both directions. Since August 1969 there have been six major price swings lasting an average 7.9 years and seeing a typical change in the value of the US dollar of some 67%." Howard Friend CMT
Howard continues on the historical political risks, "Since President Nixon scrapped the Bretton Woods Agreement in 1971 and in particular since the late 1980s there has been a clear bias for Republican Administrations to preside over a weaker currency. The US dollar has declined in value by close to 14% over the combined terms of Republican Administrations while it has risen by an average of 15% when Democrats have been in power."
There you go, you now have 2-sides: Long-term cycles and Political