Nyhan contends that "journalistic claims about 'turning points' are best understood as metaphors that are used to used to manufacture dramatic narratives":
It's possible, of course, that the Tucson shootings or the president's response to it will have some small effect on our nation's politics, but the idea that it will restore civility or decrease polarization is implausible. What's more likely is that the president's speech in Arizona and/or his State of the Union address will be framed as "turning points" if the economy improves and Obama wins re-election in 2012. If the economy continues to perform poorly and he loses, however, some other "turning point" will be selected to "explain" his defeat (the outburst of anger against health care reform in summer 2009, the Republican landslide in the midterm elections, etc.) -- whatever best fits the narrative.