President Donald Trump begins his conflict with Iran on a narrow ledge in public opinion. So long as the mission’s costs to America remain small, he’s unlikely to face insurmountable political pressure to end it. But he starts the war extraordinarily vulnerable to backlash if things go wrong.

Polls show that most Americans do consider the Iranian nuclear program a threat. But in one January survey, 70% of all Americans (and 80% of independents) said they opposed military action in Iran. Similar proportions of both groups said any president should obtain approval from Congress before initiating military action.

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