Mohammad Bagher Zolghadr replaces Ali Larijani, who was killed last week in an Israeli strike. He has a history of expanding the Guards’ reach into Iran’s politics.

One of Ayatollah Ali Khamenei’s closest confidants, Mr. Larijani emerged as the face of the government after Mr. Khamenei was killed.

The weeklong fight over Iran’s next leader pitted the Revolutionary Guards against moderates. The generals won, but only over spirited resistance.

Opponents of the government, however, worried the new supreme leader, a son of the recently killed Ayatollah Ali Khamenei, would rule with an iron fist like his father.

Ali Larijani, the head of Iran’s Supreme National Security Council and a close confidant of Ayatollah Ali Khamenei, said Iran was determined to avenge the killing of the leader.

The Islamic Republic is aiming to draw out the conflict and broaden the fighting. That would force President Trump to risk more casualties and more political capital.