Former White House press secretary Sarah Sanders on Thursday apologized to former Vice President Joe Biden after mocking a debate moment where Biden -- who has been open about overcoming his own stutter -- appeared to imitate a stuttering child to relay how he connects to people.

Sanders' apology came after she tweeted, "I I I I I I I I I I I I I I I hhhave absolutely no idea what Biden is talking about," prompting the former vice president to tweet, "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."

"I actually didn't know that about you and that is commendable," Sanders said in response. "I apologize and should have made my point respectfully."

Sanders deleted the original tweet.

Biden has long been open about overcoming his stutter to become an effective public speaker. He told The Atlantic in a recent profile that his verbal stumbles were "the best thing that ever happened" to him.

"Stuttering gave me an insight I don't think I ever would have had into other people's pain," he told the magazine.

When asked if he was concerned about President Donald Trump mocking his stutter if he becomes the Democratic nominee, Biden added, "I don't think so."

"If you ask the polls, 'Does Biden stutter? Has he ever stuttered?,' you'd have 80 to 95% of people say no," Biden said, positing that if Trump were to attack his verbal slips, "it'll just expose him for what he is."

In a 2010 appearance on ABC's The View, Biden said he would stand in front of the mirror and quote poetry to help develop a cadence. Later, in college, he said he took public speaking classes.

The former vice president entered Thursday's debate holding onto the lead in the race for the Democratic nomination with the backing of 26% of registered voters who are Democrats or Democratic-leaning independents, according to a new CNN Poll.