我曾批評過，川痞在消耗或搞垮美國國力之外，他對美國最大的傷害之一就是：搞臭了美國在國際上的「可信度」。亞希-彌珞教授這篇文章對這一點有深入分析，請參考。

此文雖然以川普政策做為「樣本」，亞希-彌珞教授所闡述的道理屬於原則性，故置於此版。

The Price of Unpredictability

How Trump’s Foreign Policy Is Ruining American Credibility

Keren Yarhi-Milo, 10/02/25

For decades, U.S. foreign policy has depended on credibility: the belief that Washington would honor its commitments and that its past behavior signaled its future conduct. The United States, for instance, was able to develop a large network of allies because its partners trusted that, if attacked, Washington would defend them. It could strike free-trade deals with countries around the world and negotiate peace agreements because, generally speaking, it was seen as an honest broker. That is not to say the United States has never surprised, or that it never reneged on a promise. But for most of its modern history, it has been a trustworthy actor.

But unlike any U.S. president before him, Donald Trump has abandoned all efforts to make Washington reliable or consistent. His predecessors had also, at times, made decisions that undermined American credibility. But Trump’s lack of consistency is of an entirely different magnitude—and appears to be part of a deliberate strategy. He proposes deals before backing down. He promises to end wars before expanding them. He berates U.S. allies and embraces adversaries. With Trump, the only pattern is the lack of one.

Trump’s theory of the case is simple. By keeping friends and foes off balance, the president believes he can secure quick wins, such as modest increases in European defense spending. Trump also thinks that unpredictability affords him greater wiggle room in international affairs by ensuring that allies and adversaries are always second-guessing his next course of action. Finally, Trump thinks that he can frighten and thus deter opponents by appearing unhinged—an idea that political scientists call the madman theory. As Trump once boasted, Chinese President Xi Jinping would never risk a blockade of Taiwan while he is president because Xi “knows I’m fucking crazy.”

As some analysts have pointed out, Trump’s approach has delivered a few temporary international victories. But in the long term, Trump’s approach to global politics is not likely to strengthen the country. Other states will work to flatter Washington for a time, in hopes of avoiding U.S. penalties. But eventually, governments will look to protect themselves by aligning with other countries. The United States’ list of adversaries will, accordingly, grow. Its alliances will weaken. Washington, in other words, could find itself ever more isolated—and without any clear path to reestablishing its reputation.

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U.S. presidents have consistently argued that, to protect American power, Washington’s commitments need to be credible. Harry Truman, for instance, decided to intervene on the Korean Peninsula in order to check Soviet expansionism. “I remembered how each time that the democracies failed to act, it had encouraged the aggressors to keep going ahead,” he later said, by way of explanation. Lyndon Johnson escalated the war in Vietnam largely out of fear that retreat would signal that Washington wasn’t serious about containing communism. George W. Bush justified the 2007 surge in Iraq on the grounds that withdrawal would undermine U.S. credibility; Barack Obama kept U.S. forces in the country for similar reasons. And when Obama hesitated to enforce his self-proclaimed “redline” against chemical weapons use in Syria, he was pilloried by his critics for emboldening the United States’ enemies. (He later told a journalist that “dropping bombs on someone to prove that you’re willing to drop bombs on someone is just about the worst reason to use force.”) After the botched withdrawal from Afghanistan, Joe Biden was also criticized for undermining Washington’s reputation for reliability, resolve, and competence.

What effect these leaders’ decisions actually had on American credibility is unclear. The causal relationship between a state’s decisions and the way those decisions are perceived is complex and fuzzy. The Dartmouth political scientist Daryl Press, for instance, has argued that states look to present interests and capabilities, rather than past behavior, to measure resolve. Other scholars, including Roseanne McManus, have shown that leaders’ reputations for resolve matter only under certain conditions during crises. And research I have done with the political scientist Alex Weisiger shows that countries that have backed down in the past are twice as likely to be challenged in the future. Other research of mine demonstrates that credibility is shaped as much by perceptions of consistency and reputations for resolve, built up over time, as it is by the costly signals that leaders attempt to send and how they are received by adversaries. Leaders, in other words, think back to their past interactions with adversaries in estimating intentions just as much as they take into account the actions those adversaries are taking during a particular crisis.

But when it comes to Trump, these findings are almost beside the point. Whatever it is that scholarship says a government needs to do to establish credibility, Trump is doing the reverse. The president has openly questioned the most sacrosanct of U.S. defense guarantees—NATO’s Article 5 commitment to collective defense—by declaring that if allies do not “pay up,” they cannot expect protection. He has pulled the United States out of multilateral agreements, such as the Paris climate accord and the Iran nuclear deal, without regard for reputational costs. He even reneged on the U.S.-Mexico-Canada trade deal, which he negotiated and signed during his first term. And he has flipped back and forth between criticizing and praising Russian President Vladimir Putin—one of Washington’s most determined adversaries—with no clear trigger. His recent meeting with Putin in Alaska was a case in point. It was organized hastily and meant to burnish Trump’s reputation as a dealmaker, but he got nothing concrete in return from his Russian counterpart. Most observers say the American president was played.

Trump may be aware of what his behavior is doing to American credibility, or the consequences may elude him. But either way, the reputational costs for consistency and reliability clearly do not affect his decisions. The president does not want to be credible so much as he wants to gain the psychological upper hand to score quick victories. If that requires disregarding long-standing American commitments, so be it. He wants maximum flexibility: the ability to do whatever he wants, whenever he wants to, in order to get his way.

AGENT OF CHAOS

Trump’s unpredictability is clearly intentional. The president relishes in being chaotic and understands that his threatening behavior helps achieve certain aims, such as his trade deals. “We have to be unpredictable,” Trump said when first running for president in 2016. “I don’t want them to know what I’m thinking.”

But that does not mean the president’s behavior is always attached to a strategy. Instead, it is often the byproduct of mood swings—a version of what the scholar Todd Hall calls “emotional diplomacy.” Fear, anger, disappointment, and revenge are now common drivers of American statecraft. It is a fact many countries have discovered the hard way. During his first term, for instance, Trump praised Canada’s then prime minister, Justin Trudeau, and struck a trade agreement with Ottawa. During his second, he accused the country of not doing enough to curb the flow of fentanyl and other narcotics and then hit it with a suite of tariffs. Likewise, Trump repeatedly celebrated his warm relationship with Indian Prime Minister Narendra Modi during term one, only to turn on New Delhi after it denied that Washington helped stop its May conflict with Pakistan. Ukrainian President Volodymyr Zelensky’s relationship with Trump, meanwhile, has moved in seemingly the opposite direction. At first, Zelensky incensed Trump by correcting him in a White House meeting, prompting Washington to temporarily suspend aid to Kyiv. But then Zelensky made nice, and last month, Trump declared that he supported Ukraine’s quest to take back all its land from Russia—something he previously declared unachievable.

For foreign leaders, keeping up with Trump’s shifting moods and whims is nearly impossible. But there are a few different strategies they can deploy to try to win the president over, or at least to limit the carnage. The first is flattery—feeding into Trump’s grandiose self-image. This technique has been particularly popular among Washington’s closest partners. In addition to Zelensky, for instance, NATO Secretary-General Mark Rutte called the U.S. leader a “pragmatic peacemaker” after his August meeting in the White House, almost certainly in an attempt to prevent the president from abandoning the alliance. Israeli Prime Minister Benjamin Netanyahu, meanwhile, praised Trump’s “decisive leadership” while successfully pressing him to join Israeli airstrikes on Iran. But even neutral countries have sought to play to Trump’s arrogance. Pakistani Army Chief Asim Munir, for example, nominated Trump for a Nobel Peace Prize in an effort to split the United States from India.

Flattery, however, quickly loses its value as more leaders deploy it. If every country flatters Trump, after all, none of them gain leverage. And for countries that have grown angry at being bullied, praising Trump is sometimes too unpalatable to countenance. As a result, some governments have adopted the opposite approach—confrontation. Brazilian President Luiz Inácio Lula da Silva, for example, has responded with defiance as Trump applies high tariffs to his country and sanctions its judges for convicting former President Jair Bolsonaro over his plot to steal an election. Modi has taken an aggressive line toward Trump, as well. But although these measures can help improve leaders’ popularity at home, they rarely cause Trump to back off, which can then cause domestic backlash of its own. Swiss President Karin Keller-Sutter had a confrontational phone call with Trump after Washington hit her country with massive tariffs, but when Trump didn’t budge, she was accused by her domestic opponents of mishandling relations.

There is a middle approach between flattery and confrontation: hedging. It involves being flexible and cozying up to multiple major powers, including some U.S. adversaries. Many Latin American countries, for example, are trading and cooperating more with Asia and Europe in the wake of Trump’s election while still working with Washington. Gulf monarchies flatter Trump even as they strengthen ties with China. French President Emmanuel Macron has urged Europe to pursue a course of “strategic autonomy” that weans his country and the continent off their dependence on both China and the United States.

These approaches are not mutually exclusive. Uncertain of how to respond to Trump’s volatility, much of the world flatters Trump one day, confronts him the next, and then hedges the day after. But ultimately, none of these tactics have delivered more than temporary success. Trump continues to shift his approach to the world almost minute by minute, depending on how he feels.

AT WHAT COST

To his credit, Trump has scored some legitimate achievements by being unpredictable. Consider, for example, his bombing of Iran, which set back the country’s nuclear ambitions. When asked whether he would strike Iran after Israel began its bombing campaign, he deliberately waffled. “I may do it, I may not do it,” he said. “I mean, nobody knows what I’m going to do.” The result was uncertainty in Israel and Iran about how they should position themselves. His decision to ultimately intervene militarily was driven by his desire to get rid of perceptions that he was weak and backed down when confronted, as well as by his urge to be seen as a winner. By demonstrating to other countries his willingness to flip quickly and turn on them, Trump may have thus bolstered American deterrence.

His handling of allied defense budgets could also be considered a victory. For decades, American leaders have pushed for the rest of NATO to up its military spending but never challenged Article 5. European countries thus felt relatively little pressure to act. By casting doubt on collective defense, however, Trump was able to inject some urgency, and at the 2025 Hague summit, European allies pledged to raise their defense spending to a remarkable five percent of GDP. The U.S.-European tariff standoff followed a similar script. Under threat of escalating tariffs, Brussels made trade concessions to Washington over this past summer that were once deemed unthinkable, including an agreement to purchase $750 billion worth of U.S. energy. In response, Trump declared victory. European Commission President Ursula von der Leyen, meanwhile, praised his “decisive leadership.”

But it is unclear to what extent these victories will be lasting. Trump, for example, may have coaxed more defense spending out of Europe, but at the cost of making NATO more fragile. Even though NATO members are spending more on their own security, the alliance’s strength relies primarily on its collective defense guarantees, which Trump has now weakened. After all, if the mighty United States itself will not respond militarily when a NATO ally is attacked, then the alliance will be weaker even if European countries increase their defense budgets. Trump’s tariffs on the continent tell a similar story: Washington may have extracted its economic concessions, but Europe is now increasing its economic and political autonomy. As a result, the United States will soon have less sway with the continent. In fact, it will have less sway over the whole world. As American credibility deteriorates, it may become harder for Washington to negotiate or facilitate peace deals—as it often does—which will result in a more volatile international system.

Washington will have fewer friends.

Many American politicians, including some Republicans, have warned about the long-term consequences of Trump’s chaotic global decisions. Even if he is succeeded in office by a close political ally, the next U.S. president might try to act in a more predictable manner (particularly if they are even-tempered). But reestablishing American credibility will be easier said than done. A country’s reputation extends beyond its present leader: when Trump repeatedly breaks promises or abruptly shifts course, it deepens skepticism not only about him but also about the reliability of American institutions altogether. And once credibility is lost, it is hard to recover. The next U.S. president, no matter their approach, will inherit allies who flatter but also hedge, adversaries who test and wait, and a system in which the United States’ word simply carries less weight than it once did.

Washington, in other words, will have fewer friends. For many U.S. partners, hedging will become a necessity as flattery loses its effect and direct confrontation becomes too costly. Meanwhile, Washington might acquire new adversaries, as countries spurned by Trump seek defense partnerships with American competitors. Deterrence will grow more costly, as U.S. officials contend with a growing number of threats. And Washington will have to spend more to reassure the allies it still has.

The United States might find itself with fewer close allies even without Trump, as the international system becomes increasingly multipolar. But the current president’s unpredictability is likely hastening this process. Trump may leave office convinced that his unpredictability made Washington stronger and that Americans will benefit from the resulting configurations of power and transactional deals. He may think that, by rejecting the need for credibility, he freed the United States from constraints that tied the hands of previous presidents. But history is likely to show otherwise: that Trump replaced credibility with volatility, leaving behind a United States that is less trusted.