Julián Castro questioning Joe Biden’s memory was the most tweeted exchange at Thursday’s Democratic debate and today, it is the most talked-about moment.

Mediaite covered reaction from ABC correspondent Jonathan Karl and contributor Rahm Emanuel:

“I think for Castro — he could have made the point, he had a legitimate point, but its a disqualifier the way he handled it,” Emanuel said. “It will come across as mean and vindictive. That’s not who he is.”

During the next segment, Karl joined ABC’s coverage and found that after reviewing the transcript, “Julian Castro was just flatly wrong … It seemed to me that Biden was right and that Castro mischaracterized what he said.”

And Senator Chris Coons (D-DE) said: “That kind of needless and groundless personal attack out of Julián Castro I think will be promptly rewarded with a drop in the polls.”

Now Castro has been making the rounds defending his comments. While on with MSNBC, Chris Matthews confronted Castro saying they got word ahead of time that Castro was going “to go on the attack against Biden, that it was all telegraphed.” Castro denied it (watch above). He is also denying it was a comment about age.

While Castro is defending the comment, many fellow Democrats are chiding him for it.