Trumpian unpredictability often undermines coercive diplomacy. What would have happened if the Trump administration had made clear that the use of chemical weapons against civilians in Syria would result in American military action? Or if Trump and his closest advisors hadn’t repeatedly signaled that they would rather work with Assad than against him? We will never know. But an unambiguous threat to retaliate might have deterred the use of chemical weapons in the first place.
Seen from this perspective, the American strike looks like a failure of coercive diplomacy, not a success. While Trump demonstrated his willingness to use force by attacking the Shayrat air base, the only way that the attack will reduce the chances of the Assad regime using chemical weapons in the future is if it believes that Trump is predictable and that any future use will cause another strike.
Similarly, leaks from the administration suggested that if Pyongyang tested a nuclear device last weekend, then the United States would launch military action against North Korea. Other members of the administration walked back those threats, creating — at least in public — significant ambiguity about possible American actions. On Monday, Vice President Mike Pence warned that North Korea should not test American resolve but that the United States is open to talks. Let’s say that Trump does, in fact, intend to retaliate if North Korea tests another nuclear device. The unpredictability of the situation likely makes Pyongyang more, not less, likely to initiate a test. After all, it cannot be sure that Trump would, in fact, use force.