Former chief White House Press Secretary Sarah Huckabee Sanders tweeted an apology to Joe Biden after mocking his reference to his stuttering at the sixth Democratic presidential debate.

The original tweet, which has since been deleted, said, “I I I I I I I I I I I I I I I hhhave absolutely no idea what Biden is talking about. #DemDebate.”

After an eruption of angry Twitter responses, Sanders tried to defend the comment by saying, “To be clear was not trying to make fun of anyone with a speech impediment. Simply pointing out I can’t follow much of anything Biden is talking about.”

Biden has struggled with a speech impediment throughout his life. His stutter has gained widespread attention in recent months after comments from his debate performances.

After the debate, Biden’s Twitter account said, “I’ve worked my whole life to overcome a stutter. And it’s my great honor to mentor kids who have experienced the same. It’s called empathy. Look it up.”

Deleting her original tweet, Sanders issued an apology saying, “I actually didn’t know that about you and that is commendable. I apologize and should have made my point respectfully.”

In the wake of President Donald Trump‘s impeachment in the House, a senior campaign official for Biden said before the debate, “Vice President Biden is going to spend this evening focused on his case against Donald Trump. He believes it would be a mistake for Democratic candidates to spend three hours attacking each other tonight.”

Sanders is widely expected to launch a campaign in her home state of Arkansas for governor.