Saudi Arabia’s escalating crisis with Iran, sparked by the execution of a leading Shiite Saudi cleric, is as much about domestic politics in both nations as it is about their regional tussle for domination of the Middle East.

For now, at least, the flare-up has benefited both the Saudi government and its most virulent foe, the powerful conservative elements of the Iranian regime. The additional winner has been Islamic State, as usual thriving on discord among regional powers that are supposed to be fighting it.

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