run a negative ad against another candidate. sanders does correctly criticize hillary clinton on issues and point out the differences. he's gone after clinton for not taking a position on the trans pacific partnership. he has criticized hillary clinton on her cozy position with wall street. on the key stone xl pipeline. and earlier today hillary clinton again refused to answer a question on the keystone xl pipeline. >> as president, would you sign a bill yes or no in favor of allowing the keystone xl pipeline. >> well as you know i was the secretary of state who started that process. i was the one who put into place the investigation. i have now passed it off, as obvious because i'm no longer there, to secretary kerry. this is president obama's decision. and i am not going to second