NATO did not make Mr. Rutte available for an interview. But in an interview with Reuters earlier this month, Mr. Rutte said he was aware that the way he treated Mr. Trump was widely frowned upon in Europe.
“I hear the criticism, obviously — I’m not deaf,” he said. But he also credited Mr. Trump for “taking this decisive action, to take out the capability of Iran to pose a threat as an exporter of terrorism and chaos.” He added, “If a president of a country is providing that kind of leadership, some praise is warranted.”
Mr. Rutte’s main task is to keep the 32-nation alliance together and Mr. Trump engaged, supportive and involved. As someone who does not need to face voters, Mr. Rutte appears prepared to swallow some pride in order to please the White House and maintain its willingness to provide crucial intelligence, and to sell vital arms, to Ukraine.
But Ivo Daalder, a former American ambassador to NATO, said that on Iran, “it makes no sense for the NATO secretary general to support an argument and a war that 31 other countries think is stupid, illegal, unnecessary and deeply destructive of the main goal, to weaken Russia.”
“The number one goal for him,” Mr. Daalder added, “is to keep NATO secure, and right now the biggest threat to NATO unity is Trump.”
Fabian Zuleeg, chief executive of the European Policy Center, a Brussels research organization, said working to keep the United States involved in NATO was crucial. “But as a European leader with responsibility to other European NATO members, Rutte is over the top, leaning too much in one direction,” he said.
Nathalie Tocci, a former European official who now teaches at Johns Hopkins SAIS, said Mr. Rutte appeared as “Trump’s cheerleader, and it’s not his job description, and I don’t think it’s really effective.” The only times Mr. Trump “has responded positively to Europe is when Europeans have straightened their backs,” she said. “NATO is a defensive alliance and this is not a defensive war,” she said about Iran.
George Robertson, who was NATO secretary-general from 1999 to 2003, during the Iraq war, when NATO was deeply divided, said Mr. Rutte was in a tough spot. The job is tricky, he said, especially “with 32 countries around the table and one of them disproportionately influential.”
The job of the secretary general, he said, “is to build the trust that glues the alliance together, and sometimes that means you have to defer to some countries and people when you don’t particularly want to,” he said, remembering tough times with Donald Rumsfeld, then the U.S. defense secretary. In Mr. Trump, “Rutte has a big figure who is unpredictable and at times capricious, but he has to keep the alliance together.”
Mr. Rutte, a former Dutch prime minister praised for his ability to build political coalitions, has also been criticized, though less harshly, for telling CBS that European allies “needed a couple of weeks to come together,” but that they would in time “answer the president’s call, to make sure that we secure the free sailing through the Strait of Hormuz.”
Some European nations have said they are willing to help maintain navigation there, but only after hostilities end, and discussions have not progressed as far as Mr. Rutte suggested.
Mr. Rutte has been an important voice in Mr. Trump’s ear on Ukraine and on Greenland, when the president threatened to seize the territory of a NATO ally, Denmark. And despite Mr. Trump’s view that Ukraine somehow provoked the Russian invasion of four years ago and should give up unconquered territory to secure peace, Mr. Rutte and other key European leaders have so far persuaded Mr. Trump to continue to provide vital American intelligence to Ukraine.
“I personally think Rutte is doing what he has to do,” said Fernando Adolfo Gutiérrez Díaz de Otazu, a Spanish senator and retired general who is a vice president of NATO’s parliamentary assembly. Some of the European exasperation, he said, is uttered by the same officials who “think — or pretend to think — they can secure the European continent without the cooperation of the United States,” which is not the case, he said.
Many Europeans view Mr. Rutte “as just following President Trump, without any objection and without saying anything that can disturb” him, Mr. Gutiérrez said. “It doesn’t sound very well on this side of the Atlantic, but he has to say it, I believe.”
But then he added, “I wouldn’t say it.”
Americans have mixed views of Mr. Rutte’s effectiveness, largely based on political loyalties, said Matthew Kroenig, a former U.S. defense official under Republican presidents who is at the Atlantic Council, where he studies Mr. Trump’s foreign policy.
While Republicans who support Mr. Trump “see Rutte as a terrific secretary general,” he said, Democrats and independent voters are puzzled, asking, “How can this respected European leader be saying these kinds of glowing things?”
But for Mr. Rutte to openly criticize or attack Mr. Trump, he said, “would ultimately be counterproductive for the alliance.”