Michael Cohen, who serves as special counsel at the Trump Organization, tweeted, "NBC/WSJ poll has @realDonaldTrump beating #CrookedHillary on #Honesty & #NationalSecurity. This picture says it all!"
The graphic he included in the tweet features a picture of Clinton, with the words, "I presided over $6 billion lost at the State Department, sold uranium to the Russians through my faux charity, illegally deleted public records, and murdered an ambassador. Elect me!"
Messages left with Clinton and Donald Trump's campaigns were not immediately returned.
CNN anchor Ashleigh Banfield slammed Cohen on her show Tuesday, saying: "This show is called 'Legal View' because we know a thing or two about the law, and Michael Cohen is a lawyer. That there is libel."
"To suggest that a woman murdered an ambassador. Look, it's not as though Hillary Clinton's team is about to go and launch some litigation on this, but that's pretty striking stuff," she said.
Banfield showed a tweet from 2014 of Cohen with Clinton and her husband, former President Bill Clinton, where he wrote, "#tbt being received by two great Americans...Hillary Clinton and Patrick Kennedy at the Kennedy Compound."
"Apparently Michael Cohen thought she was a great American two years after Benghazi, and now he does not," she said. "Let's just be really frank here, people. Don't call someone a murderer of an ambassador, for God's sake. It's offensive to Americans who really want the truth and what's going on in politics. Please, give us a break."
Cohen's tweet comes the same day as a the House Select Committee on Benghazi released an extensive report on the September 11, 2012, attacks that killed four Americans, including Ambassador Chris Stevens. The report from the House Republicans on the committee argues that intelligence was available suggesting an attack in the area was possible and that Clinton and a top aide, Patrick Kennedy, should have realized the risks.
Cohen's tweet came after an NBC News/Wall Street Journal poll
published Tuesday shows Trump is ahead of Clinton at "being honest and straightforward" 41% to 25% respectively and 44% to 39% on the issue of national security.