Negotiations between the US and Panama had been underway since April 2004 and were concluded with the signing just two days before the Administration's fast track authority expired. That authority permitted negotiations that would result in trade deals that Congress would approve or deny without the ability to make changes in them.
In today's US political climate, with claims that such trade deals take jobs away from working Americans, it's not clear whether this treaty will be approved. The Panamanian legislature had approved the treaty by a 58 to 3 vote. What might work in favor of the US Congress approving the deal is that Panama included provisions requiring both sides to respect and live up to international labor standards in environmental agreements.
According to the US Census Bureau, through the first five months of 2007, exports to Panama have totaled $1,336 million, imports $140 million. Estimates are that the US buys about 48% of Panama's exports and provides 27% of its imports.