White House staff secretary Rob Porter resigned Wednesday, a day after a British newspaper reported allegations from two ex-wives of physical and verbal abuse, the White House said.

Press Secretary Sarah Huckabee Sanders told reporters that it was "a personal decision Rob made," and that he "will stay on to ensure a smooth transition."

"As has always been our policy, we do not comment on security clearances. Rob Porter has been effective in his role as staff secretary. The president and chief of staff have full confidence in his abilities and his performance," Sanders said Wednesday.

Porter’s two ex-wives, Jennifer Willoughby and Colbie Holderness, told DailyMail.com in a report published Tuesday that Porter was physically and verbally abusive to them during their marriages. Willoughby said the abuse started on their honeymoon and that she filed a restraining order against Porter in June 2010 after he punched the glass on a door to their home and refused to leave, violating a separation agreement. NBC News has reached out to the women but has not yet spoken with them, nor investigated their stories.

In a statement announcing his departure Wednesday, Porter said, "These outrageous allegations are simply false."

"I have been transparent and truthful about these vile claims, but I will not further engage publicly with a coordinated smear campaign," Porter said.

Porter was an influential senior aide in President Donald Trump's administration and played a key role in writing the president's State of the Union address last month. After the allegations surfaced Tuesday, the White House strongly defended him.

“Rob Porter is a man of true integrity and honor and I can’t say enough good things about him. He is a friend, a confidante and a trusted professional. I am proud to serve alongside him," John Kelly, President Donald Trump's chief of staff, said.