John Bolton, President Donald Trump’s fired national security adviser, harshly criticized Trump’s foreign policy on Wednesday at a private lunch, saying inviting the Taliban to Camp David sent a “terrible signal” and that it was “disrespectful” to the victims of 9/11 because the Taliban had harbored al Qaeda.

Bolton also said that any negotiations with North Korea and Iran were “doomed to failure,” according to two attendees.

All the North Koreans and Iranians want to do is negotiate for relief from sanctions to support their economies, said Bolton, who was speaking before guests invited by the Gatestone Institute, a conservative think tank.

“He ripped Trump, without using his name, several times,” said one attendee. Bolton didn't immediately respond to a request for comment.

Bolton also said more than once that Trump’s failure to respond to the Iranian attack on an American drone earlier this summer set the stage for the Islamic Republic’s aggression in recent months.

At one point, Bolton, a previous chairman of Gatestone, suggested that had the U.S. retaliated for the drone shootdown, Iran might not have damaged the Saudi oil fields.

Bolton called the alleged attack on Saudi Arabia, which U.S. and Saudi officials have blamed on Iran, “an act of war” by anyone’s definition.

The former national security adviser’s comments come on the same day Trump named his successor, hostage negotiator Robert C. O’Brien.

Speaking on an airport tarmac in Los Angeles, Trump introduced his new top foreign policy aide as “highly respected” and hailed their “good chemistry.” The remarks indicated that in O’Brien, Trump sees a more compatible adviser than Bolton, whose disagreements with the president and clashes with other senior officials often spilled into public view.

After the attack in June, Trump was poised to launch a military response against the Iranians -- strongly urged by Bolton -- but pulled back after Fox News host Tucker Carlson and others warned him that it was a bad idea.

During Wednesday’s luncheon, Bolton said the planned response had gone through the full process and everybody in the White House had agreed on the retaliatory strike.

But “a high authority, at the very last minute," without telling anyone, decided not to do it, Bolton complained.

Bolton spoke to around 60 Gatestone donors at the exclusive restaurant Le Bernardin in Manhattan. Attendees included noted lawyer Alan Dershowitz and his wife Carolyn, former attorney general Michael Mukasey, Newsmax CEO Chris Ruddy, First Amendment lawyer Floyd Abrams, former Fox News host John Stossel, former New York Lt. Gov. Betsy McCaughey and New York billionaire John Catsimadis.

Billionaire Rebekah Mercer introduced Bolton as “the best national security adviser our country could have hoped for,” garnering her very loud applause. Bolton had been scheduled to speak to the group before Trump fired him.

In his talk and the Q&A session that followed, Bolton took attendees through a number of global issues.

On Afghanistan, another frequent subject of disagreement with the president, Bolton said that the U.S. should not have pursued a peace deal with the Taliban.

Instead, he said, the U.S. should keep 8,600 troops in Afghanistan with intelligence support and other support elements. He called the proposed deal that was on the table similar to the agreement the Taliban offered the U.S. after 9/11, but said “it doesn’t make any sense.”

More than once, Bolton said, Israel would “sooner or later” see a new government, even though he personally liked Israeli Prime Minister Benjamin Netanyahu.

On Venezuela, a focus of his short White House tenure, Bolton claimed there were 20,000 to 25,000 Cuban troops in the South American country. The day they left, he predicted, the Nicholas Maduro regime would fall by midnight.

He also said that if British Labour leader Jeremy Corbyn were to become prime minister, it would be “fatal to the special relationship” between the U.S. and Britain.

During the Q&A session, Dershowitz told the crowd that it was “a national disaster” that Bolton had been booted from the White House, to what the attendee described as “thunderous applause.”