Wendy Sherman, former undersecretary for political affairs during the Obama administration and lead U.S. negotiator for the Iran nuclear agreement, said Thursday that President Donald Trump is to blame for this week’s attack on the U.S. Embassy in Baghdad, Iraq, by pro-Tehran forces.

In a USA Today op-ed, Sherman asserted President Trump’s withdrawal from the nuke deal has ushered in a “combustible moment” in the Middle East and accused of the president of “diminishing” the State Department’s diplomatic efforts in the region.

“Even some of the harshest critics of the Iran nuclear deal now understand that the perfect is, indeed, the enemy of the good; that in volatile international situations, solid, incremental progress trumps chaos,” Sherman wrote. “The Iran nuclear deal was meant to prevent Iran from getting a nuclear weapon, since such a capability would project even greater Iranian power in the Middle East and deter the ability of Washington and its allies to build a lasting peace in the region.”

“Three years into his presidency, Donald Trump owns the events and outcomes in Iraq and Iran, as he does in North Korea, Afghanistan, Venezuela, the Middle East, Russia, China and Hong Kong,” she added. “Having diminished our State Department, intelligence agencies and military, the very institutions that could have helped him construct an effective national security and foreign policy, he is now on his own.”

President Trump fulfilled one of his key campaign promises by removing the U.S. from the Iran deal in May 2018 and has since taken a stronger approach to the world’s biggest bankroller of terrorism.

Sherman’s op-ed comes after pro-Iran militiamen withdrew from the U.S. Embassy compound in Baghdad on Wednesday. The move came after the Department of Defense deployed an additional 750 soldiers to protect the besieged buildings.

On Tuesday, President Donald Trump directly blamed Iran for orchestrating the attack and threatened it will pay a “very big price.”

“The U.S. Embassy in Iraq is, & has been for hours, SAFE! Many of our great Warfighters, together with the most lethal military equipment in the world, was immediately rushed to the site. Thank you to the President & Prime Minister of Iraq for their rapid response upon request,” the president wrote on Twitter.

“Iran will be held fully responsible for lives lost, or damage incurred, at any of our facilities. They will pay a very BIG PRICE! This is not a Warning, it is a Threat. Happy New Year!” he added.

The attack on the embassy came after the U.S. launched airstrikes in Iraq against the Iranian-backed militia group Kataib Hezbollah, resulting in the death of 25 people. The strike came in response to a U.S. contractor being killed in a rocket attack.