Iran’s ambition is to be the dominant state in the Persian Gulf and an indispensable regional power in the broader Middle East. This is a plausible aspiration. Iran’s potential assets include a large population, a central geographic position, and a wealth of hydrocarbon resources. Despite facing favorable regional circumstances after 2001, however, Iran failed to fulfil this ambition. Iran’s power is brittle: its conventional military is increasingly obsolescent, its economy is strangulated by sanctions and mismanagement, and the country is more diplomatically isolated than it has been for decades. Iran has mostly developed a narrow power base that enables it to engage in spoiling tactics and to deny opportunities to its adversaries. As a result, Iran’s influence—its ability to actually shape the regional environment in the direction it favors—is heavily constrained.