Iran is using its proxies in Iraq, Syria and Yemen to increase pressure on U.S. interests in the Middle East as it seeks to build leverage before renewing negotiations with Washington. But even if U.S. talks yield sanctions relief, Tehran remains unlikely to abandon its powerful militia network. On Feb. 26, the administration of U.S. President Joe Biden launched airstrikes against Iranian-backed Iraqi militias in Syria. The strikes, which were the Biden administration’s first military action since taking office, were intended to send a message to Iran as the two governments approach possible negotiations on U.S. sanctions and Iran’s nuclear program. Biden even told reporters that the airstrikes sought to communicate to Iran that it could not act with “impunity.” But the airstrikes also functioned as a direct response to the growing threat Iraqi militias pose to U.S. forces in the Middle East, underscoring how proxy theater activity is both a...