Unpredictability has been an essential part of Donald Trump's method of conducting foreign policy. The American president raises the ceiling of threat, pushes his adversary toward believing he is ready to go further than expected, then opens the door to negotiation or steps back from escalation when he judges that doing so serves his aim.
The method has often won him a negotiating advantage. But today it raises a different question: what happens when it is no longer adversaries alone who cannot anticipate the next American move, but allies as well?
This new condition is inseparable from a wider shift in American foreign policy that predates Trump — one built on reconsidering the scale of external commitments and requiring allies to carry more of the burden of their own security. Trump pushed that shift further and added to it a greater volatility in the handling of crises and alliances. Hence the need to distinguish between a broad direction in American policy and the manner in which the president is conducting it.
The war with Iran lays the dilemma bare. Over the recent period, the administration has moved repeatedly between threatening broad military escalation and giving diplomacy another chance. Here, the difference between strategic ambiguity and volatility in policy becomes clear. The first can be an instrument of strength when the fundamental objectives and commitments are clear, while the means, the timing, and the limits of force remain unpredictable, so that the adversary is driven to reckon with the worst. But when it becomes hard to tell whether a threat and the retreat from it are merely tactical or reflect a change of objectives, uncertainty is no longer confined to the means; it reaches the direction of the policy itself, and may turn from an instrument for unsettling the adversary into a source of anxiety for the ally.
The effects of this approach differ between adversaries and allies. Iran can treat American uncertainty as part of the confrontation, testing the limits of the threat and adapting to them.
Allies, by contrast, need a measure of certainty about American policy in order to build their own security calculations. In Europe, doubt about the durability of the American commitment generates pressure to strengthen defense capabilities and reduce dependence on Washington.
These anxieties do not produce the same response in every ally. Europe is seeking to take on greater responsibility for its own security; the Gulf states are moving to build their own capabilities and diversify their security partnerships.
Israel, for its part, seeks to preserve a wide margin of freedom for its military action while shaping American decision-making, so as to narrow the gap between its security calculations and Washington's priorities.
Trump may read this trend as proof of his policy's success, since allies' efforts to build capabilities and widen partnerships accord with the aim of redistributing the burdens of security. But the paradox begins when burden-sharing turns into hedging against American policy itself. For an ally to build up its capabilities in order to share the burden with Washington is one thing; to do so in order to need Washington less, should American policy change, is another. Washington may thus end up with allies who are more capable and less dependent, but also more independent, and readier to make choices that do not necessarily match its own.
The deeper challenge lies in the effectiveness of the policy. Unpredictability may give Washington room to maneuver so long as it is part of a clear strategy; but repeating the same pattern without arriving at a clear strategic objective may cost it the capacity to surprise and to deter, give the adversary the chance to adapt, and leave allies facing still greater uncertainty about the direction of American policy.
American power rests not on military superiority alone, but on the credibility of its commitments and its alliances. The challenge is to keep adversaries uncertain about Washington's means without leaving its allies uncertain about its strategy. If the tactic becomes predictable and the strategy obscure, the politics of uncertainty may lose its advantage with adversaries and allies alike.
