On the daily chart, we see the May-September sell-off which was caused by the Fed stating it was going to begin to taper it's bond buying program. During this sell-off, the market lost a little over 9%. But from September to the beginning of November a small rally occurred. There are two reasons for this. First, we have a natural counter-rally to the sell-off, as some traders thought the sell-off was overdone and subsequently buy at what they perceive to be as value levels. At the same time, some of the overall economic numbers were printing at weak levels, which implied the Fed wouldn't be tapering as soon as thought.
However, last week we had two important reports: GDP printed at 2.8% and the employment report printed at a little over 200,000 jobs created. This indicated the economy had withstood the shutdown in fairly decent shape, which implies the underlying economy is in fact far stronger than anticipated. As a result, the IEFs broke their short-term trend line from the September-early November rally.
These charts are all saying the same thing: if you're going to short treasuries, now's the time.