Fallout from Porter's resignation

(CBS) -- President Trump answered questions for the first time about ousted white house staff secretary Rob Porter, on Friday.

"It was very sad when we heard about it, and certainly he's also very sad," the president said.

Porter resigned Wednesday after allegations against him became public.

Both of Porter's ex-wives have reported he physically abused them. The president says he recently found about the claims.

"He did a very good job when he was in the White House...As you probably know, he says he's innocent. And I think you have to remember that."

Former Vice President Joe Biden blasted the comments.

"I just read before I walked on stage, the statement from the president saying he wishes him luck. He has so much talent. That's like saying 'That ax murderer out there, he's a great painter'," Biden.

The administration is already under fire for its handling of the allegations, and the timeline for who knew what and when continues to take shape.

CBS News has learned Porter told counsel Don Mcgahn over a year ago that his security clearance background check might include derogatory information.

The FBI sent a file including the claims to the White House in June.

Then in November, Porter's ex-girlfriend called Mcgahn to tell him about the abuse allegations.

Mcgahn passed some information to Chief of Staff John Kelly, but the white house insists kelly only became "fully aware" of accusations against Porter on Wednesday.

Initially, Kelly defended Porter, but in an email to staff Thursday night, he condemned domestic violence.