President Trump has a new rule for America's partners: Cross him in one theater, and the consequences will follow you into the next.Why it matters: Trump has spent his second term battering U.S. allies, humiliating their leaders and using decades-old security relationships to settle personal and political scores.The Iran war has only deepened those impulses: Trump is growing angrier at allies that stayed out of the conflict — and punishing them as he struggles to end it.Zoom in: South Korea — recently hailed by Defense Secretary Pete Hegseth as a "model ally" — is the latest and most surprising casualty in Trump's retribution campaign.On Sunday, Trump ordered the Pentagon to "substantially reduce" the annual Ulchi Freedom Shield exercises, citing their cost and his "very good relationship" with North Korean dictator Kim Jong Un.The joint drills have served for half a century as a pillar of the deterrence architecture binding Washington and Seoul against a nuclear-armed North Korea.Trump noted in his Truth Social announcement that he "recently asked the President of South Korea if they would like to join us in the Denuclearization of the Islamic Republic of Iran, and they said, 'No thanks!'""We can't go around and protect all of these countries, especially when they're not there to help us," he told reporters Monday.Zoom out: For years, Europe has borne the brunt of Trump's assault on American alliances. As the Iran war has widened those transatlantic fractures, his pressure campaign has taken on a more systematic form.Bloomberg reports the Pentagon has sent NATO allies a survey probing their loyalty to Trump's foreign policy as it weighs where to keep — or withdraw — U.S. troops.The questionnaire ranges from support for U.S. operations and military access to weapons purchases. Most pointedly, it asks whether each country has "shown alignment" with the Trump administration's approach to foreign policy.Between the lines: Allies that have departed from that submissive posture have already paid a price.The Pentagon moved in May to withdraw roughly 5,000 troops from Germany after Chancellor Friedrich Merz publicly savaged Trump's Iran strategy.Trump threatened to cut off all trade with Spain after Madrid denied U.S. base access for strikes on Iran. Weeks later, Reuters reported that a Pentagon official had floated suspending Spain from NATO altogether.Even Oman — the key intermediary trying to broker a Hormuz deal — is now in Trump's crosshairs. He threatened Monday to "bomb the sh*t out of" the longtime U.S. partner if it "gets in the way" of an agreement with Iran.The big picture: The same war fueling Trump's fury at U.S. allies is also exposing the limits of American hard power.The 60-day deadline Trump and Iran set for a final peace deal expired Monday with no agreement — and the two sides further apart than when they signed their June memorandum of understanding.The Strait of Hormuz remains a stubborn monument to that impasse after months of U.S. military and economic pressure, even as Trump insists the waterway is "open" and could become a U.S. territory.Amid the growing strain, the Navy is pulling the USS George Washington from the western Pacific to relieve the long-deployed USS Abraham Lincoln, temporarily leaving Asia without a U.S. carrier.What they're saying: "President Trump has successfully made America respected again, and the results speak for themselves – nine wars have ended, hostages have been freed from Gaza, trade deals are fairer, and now, Iran will be prevented from ever possessing a nuclear weapon," White House spokesperson Anna Kelly said in a statement."At the same time, the President will never allow the United States to be treated unfairly, and he is righting decades of wrongs of his predecessors by ensuring all of our diplomatic relationships are reciprocal."The bottom line: Trump is teaching America's partners to prepare for a world in which Washington may not be there when they need it.That gives them every incentive to hedge against the U.S. — and gradually erodes the network of relationships that has amplified American power for generations.