Bernie Sanders has captured the minds of generation, but that doesn’t mean he’s immune from making a pretty serious blunder. According to a report from Vox, the Vermont Senator and 2016 presidential candidate was blasted after making a joke about the “mental health” of Republicans during the most recent democratic debate against Hillary Clinton in Flint, MI.

“You know, we are, if elected president, going to invest a lot of money into mental health. And when you watch these Republican debates, you know why we need to invest in that,” Sanders told the audience during the debate.

The joke was light-hearted enough, but it’s not surprising that a huge number of Americans were rubbed the wrong way. The Ruderman Family Foundation issued a statement in response to Sanders’ comments, saying that millions of Americans struggle with issues surrounding mental health every day, and that making a cheap jab at an opposing political party at their expense was entirely inappropriate. The organization’s president, Jay Ruderman, officially asked Sanders to issue an apology.

Indeed, mental health is no small issue in the United States. The CDC defines mental health as “a state of well-being in which the individual realized his or her own abilities, can cope with the normal stresses of life, can work productively and fruitfully, and is able to make a contribution to his or her community.” Shockingly, based on CDC estimates, only 17 percent of American adults are in a state of good mental health. The most common mental health issue facing Americans is depression, affecting 26 percent of all U.S. adults.

Ruderman came out in full defense of the millions of Americans that take mental health seriously. “When millions of Americans deal with issues of mental health it was highly inappropriate for Senator Bernie Sanders to use a real disability as a joke in last night’s Democratic presidential debate. He should issue an immediate apology to Americans with mental health disabilities,” Ruderman wrote.

Ruderman pointed out that Bernie Sanders wasn’t even the only presidential candidate who brought up mental health in an offensive manner. Because nearly 20 percent of Americans fall under the category of people with mental health issues, Ruderman argued that they deserve just as much respect as someone who is presumably in a good mental state. Sanders has issued no formal apology yet.