White House spokesman Raj Shah said Thursday the White House "could have done better" over the last few days when it came to "dealing with" the domestic violence allegations against former top aide Rob Porter.

"I think it's fair to say we all could have done better dealing with this over the last few days," he said.

Senior aides to President Donald Trump knew for months about allegations of domestic abuse levied against Porter by his ex-wives, even as Porter's stock in the West Wing continued to rise, multiple sources told CNN on Wednesday. Porter's ex-wives detailed the allegations to the FBI over the course of a routine background check, they told CNN's MJ Lee.

By early fall, it was widely known among Trump's top aides -- including chief of staff John Kelly -- both that Porter was facing troubles in obtaining the clearance and that his ex-wives claimed he had abused them. No action was taken to remove him from the staff.

Porter was "operating on an interim security clearance" but his clearance was never "denied," Shah said.

Shah added that the allegations are "serious and disturbing," but the spokesman also repeatedly noted that Porter denied wrongdoing.

"It is important to remember that Rob Porter has repeatedly denied these allegations and done so publicly. That doesn't change how serious and disturbing these allegations are. They are upsetting," Shah said. "The investigation does not stop when allegations come to light, it continues to determine the truth."

He added: "We should not short circuit an investigation just because allegations are made unless they compromise national security or interfere with operations of the White House. The truth must be determined."

He said that "no waivers and no special treatment" was given to Porter during the credential process.

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