Sentence:  That stunning defeat effectively ushered in a three-year deep freeze on any discussion of climate in Congress, an era of paralysis so pervasive that in June 2013, in what many environmentalists hailed as a milestone for action on climate and critics decried as a <WSD>millstone</WSD> around the neck of a struggling economy. 
Meaning of the word marked with <WSD> tags:  "Often in" '''a millstone round one's neck''' (referring to Matthew 18:6 in the Bible): a heavy responsibility that is difficult to bear.