Former U.S. Ambassador to the United Nations John Bolton said in an op-ed that White House officials have closed him off from offering policy advice to President Trump, including a way to exit the Iran nuclear deal.

In an op-ed published in National Review, Bolton said former White House chief strategist Steve Bannon, who left the White House on Aug. 18, asked him in July to draft a proposal for how the U.S. could leave the Iran deal.

But Bolton said it's unlikely his five-page plan, titled "Abrogating the Iran Deal: The Way Forward," will make it to Trump's desk, as "staff changes at the White House have made presenting it to President Trump impossible."

"Although he was once kind enough to tell me ‘come in and see me at any time,' those days are now over," Bolton wrote Monday. "If the president is never to see this option, so be it. But let it never be said that the option didn't exist."

Trump often condemned the Iran nuclear deal, negotiated by former President Barack Obama, while on the campaign trail. But in July, Trump and his administration certified to Congress that Iran was complying with the deal's terms.

According to Bolton, the president asked his advisers for "alternatives to acquiescing yet again in a policy he clearly abhorred" before the July certification, but they didn't provide the president with any options.

Bolton said his five-page plan, however, can be expanded to provide Trump with a detailed roadmap to exiting the Iran deal, and said the administration doesn't need to wait until October, the next upcoming certification deadline, to do so.

"Trump can and should free America from this execrable deal at the earliest opportunity," he said.