U.S. President Donald Trump is considering revoking the security clearances of a half-dozen former Obama administration officials and critics of his presidency.

White House spokesperson Sarah Sanders said Monday that the president is "exploring the mechanisms" to strip clearance from former CIA director John Brennan as well as five other former top national security officials: former FBI director Jim Comey, James Clapper, Michael Hayden, Susan Rice and Andrew McCabe.

Sanders accused the officials of having "politicized and in some cases monetized their public service and security clearances" by "making baseless accusations of improper contact with Russia or being influenced by Russia."

"The fact that people with security clearances are making these baseless charges provides inappropriate legitimacy to accusations with zero evidence," she said.

Sanders did not cite specific comments made by any of the officials. But the president has been seething over the backlash to his meeting last week with Russia's Vladimir Putin and the ongoing investigations into Russia's meddling in the 2016 election, whether his campaign aides were involved in the effort and whether he obstructed justice.

Rep. Adam Schiff of California, the ranking Democrat on the house intelligence committee, tweeted that "politicizing security clearances to retaliate against former national security officials who criticize the President would set a terrible new precedent."

"An enemies list is ugly, undemocratic and un-American," he added.

Former CIA directors and other top national security officials are typically allowed to keep their clearances, at least for a period, so they can be in a position to advise their successors. At least one of the former officials, ex-FBI deputy director McCabe, does not currently have security clearance, his spokesperson said.

The Washington Post reported Monday that Comey also no longer has security clearance.

Republican Sen. Rand Paul of Kentucky tweeted earlier Monday that he was planning to raise the issue of revoking Brennan's clearance at a meeting with Trump.

Just got out of WH meeting with <a href="https://twitter.com/realDonaldTrump?ref_src=twsrc%5Etfw">@realDonaldTrump</a>. I restated to him what I have said in public: John Brennan and others partisans should have their security clearances revoked. —@RandPaul

While standing next to Putin, Trump had openly questioned his own intelligence agencies' conclusions that Moscow was to blame for meddling in the 2016 U.S. election to help Trump and seemed to accept Putin's insistence that Russia's hands were clean.

Hayden tweeted Monday that a revocation of his security clearance wouldn't "have any effect on what I say or write."

And Melissa Schwartz, a spokeswoman for McCabe, tweeted that his security clearance was deactivated when he was terminated in March 2018, "according to what we were told was FBI policy."

"You would think the White House would check with the FBI before trying to throw shiny objects to the press corps..." she wrote.

Andrew McCabe's security clearance was deactivated when he was terminated, according to what we were told was FBI policy. You would think the White House would check with the FBI before trying to throw shiny objects to the press corps... <a href="https://t.co/ZOKJDChpeP">https://t.co/ZOKJDChpeP</a> —@MSchwartz3

Unprecedented move

Experts appeared split on whether the president has the authority to terminate a security clearance unilaterally.

"It's a disputed question. There is a school of thought which holds that the president has complete and exclusive authority over security clearances," said Steven Aftergood at the Federation of American Scientists' Project on Government Secrecy. "Others argue that that's not so and that the president is limited by congressional power and legislative requirements."

But they agreed that a president asking to revoke the clearance of a political critic would be unprecedented.

John V. Berry, an attorney who represents federal intelligence agency employees, said such a move would "be terrible for America" and totally defeat the process of defending national security."

"It would be horrendous. I just can't imagine that you want to go down that road," he said, adding: "If we start interjecting politics into this, our country's going to be significantly weakened."

"Legalities aside, it seems like a terrible mistake to use the security clearance system as an instrument of political vendettas," added Aftergood. "The very idea is repugnant."

The No. 2 Republican, Sen. John Cornyn of Texas, said Monday that he can understand Trump's aggravation at some former officials who "have obviously donned the uniform of the opposition team." But he says, "I don't know whether they've been abusing their security clearance at all. That's a very serious allegation."

The top Democrat on the House foreign affairs committee, Rep. Eliot Engel of New York, says revoking the clearances would be "ironic" considering the questions raised about granting them to Trump's family.

He says, "For them to start pointing fingers is ridiculous."