Mike Waltz’s ouster from the post of national security advisor followed months of White House frustrations over policy differences, particularly Iran strategy, per a Saturday report in the Washington Post.

Sources said Waltz’s addition of Jeffrey Goldberg, editor-in-chief of the Atlantic, to a Signal chat with sensitive national security information was the last straw in an already rocky relationship.

Per the report, Waltz’s coziness with Israeli officials and eagerness to use military force clashed with President Donald Trump’s preference for diplomacy:

“If Jim Baker was doing a side deal with the Saudis to subvert George H.W. Bush, you’d be fired,” a Trump adviser said, referring to Bush’s secretary of state. “You can’t do that. You work for the president of your country, not a president of another country.”

Waltz is Trump’s nominee for UN ambassador. In the interim, Secretary of State Marco Rubio is serving as national security advisor.