Johnson, the Libertarian presidential candidate, was asked about Aleppo, a Syrian city hit hard by the country's civil war, during an interview on MSNBC's "Morning Joe." "What is Aleppo?" Johnson responded, prompting criticism and a pledge by Johnson to "get smarter."
The former New Mexico governor has garnered about 9 percent support in recent four-way polls involving Democrat Clinton, Republican Trump and the Green Party's Jill Stein, according to Real Clear Politics. Clinton generally fares worse in polls that include Johnson, or both Johnson and Stein, than in those tracking her versus only Trump.
There is no guarantee that support for Johnson will fall significantly after the gaffe, especially in a race where most voters hold unfavorable views of both Clinton and Trump. But if Johnson's polling standing should drop in response to the blunder, Clinton may sap more of that support in a tightening race.
"His presence in the race in a small way has hurt Hillary more than it hurts Trump. You have to assume that any ground he loses will help Clinton," said Tim Malloy, assistant director of the Quinnipiac University poll, which last month showed Clinton with a narrower lead when the third-party candidates were included.
While he draws considerably less support than Clinton or Trump, the backing of Johnson voters could prove even more crucial to Clinton and Trump, who are now in a close contest. Clinton's lead has narrowed to only 2.1 points in an average of recent four-way polls, versus nearly 4 points a week ago.
She holds a slightly larger 2.8-point lead in recent polls tracking a head-to-head matchup with Trump. Her lead has consistently been smaller in four-way surveys than in those gauging support for just Clinton and Trump. Johnson has garnered roughly three times more support than Stein.
Still, it remains to be seen whether the Aleppo confusion will drive voters away from Johnson at all. In addition, even if support for him does fall, there is no guarantee it will shift votes to the major party candidates in a meaningful way.