In those discussions, Mr. Trump broached the idea of attacking Iran to force it to stop growing its nuclear program. Such an attack would be a significant blow to President-elect Joseph R. Biden Jr., who wants to revive the 2015 Iran nuclear accord, the signature foreign policy achievement of the Obama administration that Mr. Trump pulled out of in 2018. Such a strike on the eve of a new administration could poison relations with Tehran so much that reviving the deal would be impossible.
A strike in retaliation for rocket attacks in Iraq could also harm future relations, though most likely not as much as a strike on an Iranian nuclear facility, a Defense Department official said. But the official, speaking on the condition of anonymity because the White House meeting was private, said that the decision coming from that meeting on Wednesday was to stick to stern verbal warnings for now.
Since Mr. Trump dismissed Mark T. Esper as his defense secretary last month, along with other top Pentagon aides, Defense Department and other national security officials have privately expressed worries that the president might initiate operations, whether secret or overt, against Iran and other adversaries at the end of his term.
Officials say a strike could be inevitable if any Americans are killed before Inauguration Day. The officials have been especially nervous about the Jan. 3 anniversary of the American strike that killed Maj. Gen. Qassim Suleimani, the commander of Irans elite Quds Force of the Islamic Revolutionary Guards Corps, and the Iraqi leader of an Iranian-backed militia deaths that Iranian leaders regularly insist they have not yet avenged.
In Iraq, rocket attacks that the United States has long said were linked to Iran are a staple. But Pentagon officials worry that any uptick in such attacks could give Mr. Trump a reason to retaliate. The United States will hold Iran accountable for the deaths of any Americans that result from the work of Iranian-backed militias, the Central Command statement said.