As he pursues major foreign policy priorities over the coming weeks, President Trump must be wary of entangling the U.S. in a four-front conflict. That possibility is unlikely, but not as unlikely as some believe.

In mid-May, Trump will almost certainly withdraw from the Iran nuclear deal. If Trump then sanctions European multinationals operating in Iran, Revolutionary Guard-aligned hardliners may bite back against U.S. interests. Preparing to counter any such action and constrain escalation will require a formidable U.S. military presence in the Persian Gulf.