The ridiculous claims about climate change consequences (Bob Doppelt for example) have undermined public perception of the scientific evidence. 
  The tax, spend and regulate policies of Obama resulted in a stagnant economy and huge increases in permanent unemployment as well as $10 trillion of additional debt and shattered any illusions of a Keynesian big goverment solution to economic ills. 
So to do the proposed gun regulation claims appear as simplistic, ineffectual, despotic and sometimes risible (Charles Dalton's claim that the 2nd amendment is about white supremacy).