WASHINGTON — If partner countries helped crack down on Iranian missile violations, it could persuade President Donald Trump to sustain the Iran nuclear deal, the US ambassador to the United Nations said.Nikki Haley made her remarks on Monday after leading a White House meeting of the 15-member UN Security Council and Trump.“They’re starting to realize, ‘If we don’t start talking about the violations, if we don’t call them out, then the US is going to say this whole thing is a sham,’” Haley told the Associated Press, speaking of the other council members.Haley said that were other countries to focus on Iranian violations of Security Council resolutions on missile development and use, it could sway Trump to stay in the deal.If true, that would represent a significant shift in Trump’s approach to the 2015 deal, which has been to insist that it must be changed or the United States will pull out. Violations of existing Security Council resolutions on ballistic missile development were not part of the original deal, which was negotiated under President Barack Obama. The deal swaps sanctions relief for rollbacks in Iran’s nuclear program.At least three of the parties to the deal — France, Britain and Germany — have said they are willing to toughen sanctions on Iran outside the framework of the deal, including those targeting its missile development.Among other changes to the agreement, Trump has said previously that he wants Iranian missile development to trigger new sanctions. He also has said he wants to remove “sunset” clauses that lift some of the restrictions on Iran enriching fissile material in 10-15 years. Trump has until April to decide whether to keep the United States in the deal. At that point he must decide whether to continue to waive nuclear sanctions, as required by the pact.The Security Council delegation also toured the US Holocaust Memorial Museum, focusing on its exhibit recounting the atrocities committed during the ongoing Syrian civil war.