After President Trump announced Tuesday that the U.S. would be leaving the Iran nuclear deal, fulfilling a longtime campaign promise, Iran's supreme leader called the president's decision "a mistake." Critics say the withdrawal leaves the U.S. with no Plan B on Iran. CBS News national security analyst and former acting CIA director Michael Morell told "CBS This Morning" on Wednesday there is a Plan B – it just happens to be "very, very risky."

"There's clearly a Plan B which is put enough pressure on the Iranians, and we're going to need the Europeans to do that. So [National Security Adviser John] Bolton is going to have a conversation with them. Put enough pressure on them to bring them back to the negotiating table and get a better deal. That's the plan. The issue is that it is very, very risky to see whether or not that's going to happen," Morell said.

One of the high-stakes possibilities following the pullout is whether or not Iran will consider restarting its nuclear program and what countries might follow suit. Earlier this year, Crown Prince Mohammed Bin Salman of Saudi Arabia told "CBS This Morning" co-host Norah O'Donnell that if Iran developed a nuclear bomb, his country would do the same. Morell has "no doubt" the Saudis, a major regional rival to Iran, would follow through on that and also said it would be likely that Egypt and the United Arab Emirates would, too.

"The Iranians have a decision to make. The ball is in their court. If they stick with the deal, then they can continue to get economic benefits from the rest of the world. And if they don't stick with the deal, if they go back to their program, then the rest of the world will likely re-impose sanctions as well," Morell said.

Morell added that when the U.S. first put sanctions on Iran, it wasn't enough to bring them to the negotiating table. The Europeans, Chinese, Japanese and others had to do the same to have an impact.

"So if it's just the U.S., I'm concerned there won't be enough pressure there and the Iranians -- the Iranians will decide whether or not that happens," he said.

There are also concerns over how the withdrawal will affect the planned talks between the U.S. and North Korea where the subject of the North's denuclearization is expected to be on the table. Some say the North Koreans may be less likely to make a deal with the U.S. if they're worried the next administration might abandon it. But Morell disagrees.

"I actually agree with the national security adviser (John Bolton) that this puts more pressure on North Korea to come up with a better deal than they would have come up with otherwise," he said.