I think I understand. When the dollar goes up, there is no relationship to the trade deficit. When the dollar goes down, of course the decline is caused by the trade deficit.
Is that the logic you're using?
Nope, just that other factors are temporarily masking and indeed overwhelming the core fundamentals. When China buys U.S. treasuries and other debt, it isn't because they need a place to park the money and realize a bigger return than elsewhere...if they wanted a bigger return...there is no better place for them to put their money than in their own country. Just ask the outsourcers.
Using the principle of Occam's Razor, the best explanation is state interference...simply that they needed to prop up the dollar as part of their currency peg operations, and this was an optimal method.
The continual and accelerating drag on the dollar's value represented by the accelerating trade deficit to China and its intermediaries [call it the force of gravity] , is neutralized vis-a-vis China by their state bank interference. This allows the dollar valuation to be more directly influenced by other, perhaps less tangible, factors. Hence, the U.S. dollar was freed to rise, with the drag being neutralized, by normal investment flows, or governmental inflationary/deflationary behaviors, or even as the beneficiary of being a transhipment point for Chinese production, with middle-man profits tacked on... and so on.
That is all that happened. But absent the neutralization against the drag...it could not have happened.
A possible driving factor that could overwhelm the postulated masking effect of state interference, explaining the falling dollar against the basket of major currencies, would be the extent to which China's intermediaries who tranship China production into the U.S., and cut out the U.S. as the middleman, (this would also include European manufacturers now outsourcing to China to better compete against the U.S. middleman) have their trade surplus burgeon...while not pegging. Their currencies would rise, and eventually impact all non-pegged currencies that trade with them... including the major currencies in the basket relied upon for the measure.