President Donald Trump is considering revoking the security clearances of former top Obama administration national security officials who have made charges on Twitter and in the media about Russian collusion, as well as one former top Bush administration official.

White House press secretary Sarah Huckabee Sanders said Monday the president is “exploring” taking the security clearances of former President Barack Obama’s CIA Director John Brennan, Obama Director of National Intelligence James Clapper, Obama national security adviser Susan Rice, as well as Obama-appointed FBI Director James Comey and Andrew McCabe, who served as FBI acting director immediately after Trump fired Comey. McCabe was fired by Attorney General Jeff Sessions in March.

However, doing so could be a difficult task.

As a practical matter, many former government officials maintain security clearances as part of employment with certain government contractors, said Steven Bucci, a former Army Special Forces officer and former Pentagon official who is a visiting research fellow at The Heritage Foundation.

“Normally, people with a security clearance don’t get it revoked unless there is cause,” Bucci told The Daily Signal. “If you take one away, there has got to be a reason. It can’t just be that the president is ticked off because you said bad things about him.”

Sanders also said that the president is looking at pulling the security clearance of former President George W. Bush’s CIA Director Michael Hayden, who has also been a Trump critic regarding the Russia investigation, as well as his immigration policy.

“The president is exploring the mechanisms for removing security clearances because they have politicized and, in some cases monetized, their public service and security clearances,” Sanders told reporters.

“Making baseless accusations of improper contact with Russia or being influenced by Russia against the president is extremely inappropriate,” Sanders continued. “And the fact that people with security clearances are making these baseless charges provides inappropriate legitimacy to baseless accusations without any evidence.”

Sen. Rand Paul, R-Ky., asked Trump to consider revoking the security clearance of Brennan, who has repeatedly accused the president of “treason.”

A reporter initially asked only about Paul’s request.

“Not only is he looking to take away Brennan’s security clearance, he’s also looking to take away the clearances of Comey, Clapper, Hayden, Rice, and McCabe,” Sanders said.