Donald Trump is weighing military action in Iran over the state’s crackdown on protesters. Reports suggest that more than 600 people have been killed since the protests began in late December, with the US president saying the US military is now “looking at some very strong options”.

Trump has not yet elaborated on what these options are and has said that Iranian officials, keen to avoid a war with the US, had called him “to negotiate”. But he added that the US “may have to act before a meeting” if the deadly crackdown continues.

There is a wide spectrum of measures available to Washington should it decide to intervene in Iran. These range from diplomatic condemnation and an expanded sanctions regime, to cyber operations and military strikes. However, history weighs heavily against every move the US government may be considering.

Targeted sanctions and diplomatic pressure, which includes the 25% tariff rate recently introduced by Trump on any country that does business with Iran, remain the least escalatory tools. They allow the US to coordinate with its allies and signal moral support for protesters in Iran without triggering direct confrontation. Yet decades of experience show the limits of this approach.

Iran’s leadership has mastered how to absorb economic pressure, shift costs on to society and frame longstanding western sanctions as........

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