WASHINGTON — Former CIA director John Brennan said Sunday that he is willing to take President Trump to court to prevent other current and former officials from having their security clearances revoked, escalating a battle over whether the president is misusing the power of his office to retaliate against opponents.

“I am going to do whatever I can personally to try to prevent these abuses in the future, and if it means going to court, I will do that,” Brennan said in an appearance on NBC’s “Meet the Press.”

Brennan voiced his eagerness to challenge Trump on the same day that national security adviser John Bolton floated the idea of a sweeping review of all security clearances held by those both inside and outside the government. Such a review could affect more than 4 million Americans.

Brennan, who is among Trump’s most outspoken critics, was abruptly stripped of his clearance by the White House last week. Brennan said Sunday that since then, a number of lawyers have contacted him to offer advice on pursuing an injunction to prevent Trump from taking similar actions in the future.

“If my clearances – and my reputation, as I’m being pulled through the mud now – if that’s the price we’re going to pay to prevent Donald Trump from doing this against other people, to me, it’s a small price to pay,” Brennan said.

He did not elaborate on what such a legal move would entail.

Asked during an appearance on Fox News Channel’s “Sunday Morning Futures” about a possible lawsuit by Brennan, Rudolph Giuliani, Trump’s personal attorney, described it as a welcome opportunity.

“I would volunteer to do that case for the president. I would love to have Brennan under oath,” Giuliani said. “We will find out about Brennan, and we will find out what a terrible job he did.”

On Friday, more than a dozen former top CIA officials and a former director of national intelligence penned a statement denouncing Trump’s action against Brennan as “an attempt to stifle free speech.”

Trump told the Wall Street Journal last week that he revoked the clearance because of Brennan’s role in the “sham” Russia probe being led by special counsel Robert Mueller. That explanation appeared to contradict Trump’s earlier official statement, in which he said he took the move because Brennan “has a history that calls into question his objectivity and credibility.”

As the furor over Trump’s actions has intensified, the president has shown no signs of backing down. According to senior administration officials, the White House is preparing paperwork to strip the clearances of several other current and former officials who have either sharply critiqued Trump or have played a role in the Russia probe.

The Trump administration’s scrutiny of security clearances could extend well beyond that list, Bolton suggested.

In an interview on ABC’s “This Week,” Bolton citied an era of “unprecedented” classified leaks as justification for a formal review of individuals holding security clearances.

“I think it’s certainly appropriate, in a time when we’re seeing what I believe are unprecedented leaks of highly classified information, to look at the question of how many people have clearances, how many people received this very sensitive information, both inside the government and in the case of former officials,” he said.

Nearly 4.1 million Americans hold federal security clearances up to the “top secret” level, according to government estimates. Former officials commonly retain their clearances, some to provide advice to current administration officials and others because they hold jobs requiring clearances.

Bolton said that he did not consider a political disagreement sufficient grounds for an official to have a security clearance pulled but that violating the separation between intelligence and policy would be grounds.

He said that “senior intelligence officials, career intelligence officials who come out of the government,” should “keep that wall of separation” between intelligence and policy, and that Brennan had not done so. Bolton later added, “There is a line, and somebody can cross it.”

Trump’s stripping of Brennan’s clearance has stirred debate over whether the president followed proper procedures in making the move.

Mark Zaid, an attorney who specializes in national security law, said that under an executive order on access to classified information, Brennan may be entitled to legal representation and a written explanation of the reasons for the loss of his clearance.

“But the question is whether any agency official could realistically or legally overturn the president’s decision,” Zaid said. “So, it could be a right without a remedy.”

Civil litigation might also be possible, he said, although federal courts have been hesitant to wade into clearance disputes.

Former CIA director Leon Panetta also cast doubt on whether Trump acted in accordance with the executive order.

“I think there are questions raised as to whether or not this president has followed the executive order and whether or not he’s provided due process to those that are going to have their security clearances revoked,” Panetta said. “Yes, the president of the United States has power, but that power is limited by the Constitution and by the checks and balances in our system.”

Brennan on Sunday described himself as having “a bull’s eye on my chest,” as he continued to defend his remarks.