On 9 August 2016, the Facebook page "American Proud" posted an image purportedly showing a tweet by Hillary Clinton concerning gun control followed by a witty retort from Gary Sinise (a politically conservative actor):
Hillary Clinton: If Republicans put so much faith in the Hand of God, why do they need guns?
Gary Sinise: Because we don't trust Democrats.
Neither of the above-quoted comments is real. Hillary Clinton did not question on Twitter why Republicans need guns when they have God, and Gary Sinise did not assert that the reason was because they don't trust Democrats.
These messages don't appear on either the presidential candidate's or the actor's Twitter timelines. While it's possible that the original tweets could have been subsequently deleted, this is highly unlikely since they were supposedly retweeted thousands of times yet we found no links back to the originals.
Furthermore, this purported Twitter conversation matched an image macro posted to Twitter two months earlier:
It appears that the Facebook page "American Proud" simply re-imagined the above-displayed joke as a conversation between Clinton and Sinise.