For approximately two minutes, a fly landed on Vice-President Mike Pence's head and became an instant internet celebrity.
The phrase "the fly" has been tweeted and retweeted more than 700,000 times since it appeared during the debate.
The Joe Biden campaign has taken full advantage of this, registering the domain "flywillvote.com", while a picture of the candidate holding a fly swatter has been liked more than 500,000 times at the time of writing.
he fly has united people on both sides of the aisle, with one person labelling it "an American hero" and another calling it "probably the most memorable thing that happened".
Former senior White House adviser Kellyanne Conway called for the fly to be given a mail-in ballot, while Republican Senator Rand Paul joked it was evidence of spying as "the deep state planted a bug" on Mr Pence.
And the Merriam-Webster dictionary announced the word "fly" was trending on its website.
Myriad social media accounts have been created by people seeking to get in on the act, with one picking up more than 10,000 followers on Twitter.
Meanwhile, one person has drawn parallels to the last time a fly appeared during a presidential debate - four years ago, when it landed on the head of then-presidential candidate Hillary Clinton.
There is no suggestion that this is the same fly.