Securing Postwar Ukraine, Even With Trump’s Pledge to Help, Is Complex

President Trump has pleased Ukrainian and European leaders by promising American involvement in providing security guarantees for Ukraine if a peace settlement with Russia ever comes together.

Mark Rutte, the NATO secretary general, pronounced himself “excited” over Mr. Trump’s public commitment on Monday at a summit at the White House to some sort of security guarantee, a pledge that the Europeans have been eagerly seeking. He called it “a breakthrough.”

But exactly what those guarantees would involve remains ambiguous. Officials promised more clarity in the weeks to come as defense ministry planners come to grips with the considerable complications of turning a broad promise into realistic options.

Mr. Trump said that European countries would be the “first line of defense” in providing security guarantees for Ukraine, but Washington will “help them out, we’ll be involved.” He added later: “European nations are going to take a lot of the burden. We’re going to help them and we’re going to make it very secure,” he said.

He did not explain how.

Some involved, like Prime Minister Giorgia Meloni of Italy and the president of the European Commission, Ursula von der Leyen, spoke of an “Article 5-like” guarantee outside of NATO itself, though based on the commitment in the alliance’s charter that an attack on one member is considered an attack on all of them.

But it is hard to imagine that NATO itself would not be quickly implicated if any member state of the alliance with troops stationed in Ukraine gets into a shooting war with Russia.

Nor is it a given that Russia would change its stance and agree that troops from NATO countries could be stationed in Ukraine under a form of a de facto NATO-backed guarantee. Many analysts, like John Mearsheimer of the University of Chicago, believe that Russia’s effort to control Ukraine is based on its stated desire to stop NATO enlargement for countries Moscow considers part of its sphere, especially those that were part of the Soviet Union.

“Our goal is to ensure that we build the security guarantees together with the U.S.,” President Alexander Stubb of Finland said Monday night. “I should think that Russia’s view of security guarantees is quite different from our view.”

Russian officials rejected the idea even before Monday’s meeting. A Foreign Ministry spokeswoman, Maria Zakharova, said Russia “categorically rejects any scenario that envisages the appearance in Ukraine of a military contingent with the participation of NATO countries.”

Some European officials and analysts see Mr. Trump’s new commitment to security guarantees as a way of convincing President Volodymyr Zelensky of Ukraine to agree to Russian demands to give up the rest of the eastern Donetsk region that is not occupied by Russian forces, in order to stop the war that Russia is slowly winning. That argument suggests that what matters is a sovereign Ukraine, its future assured, even if Russia retains the 20 percent or more of Ukrainian territory it has occupied since 2014.

The territory issue did not even come up in the meeting with European leaders on Monday, according to Chancellor Friedrich Merz of Germany. Europeans were relieved, but the question has hardly gone away and underlies what may be part of a final settlement. The land that the Kremlin wants in Donetsk alone is considerably larger than the total amount of land Russia has managed to take since November 2022, and at great cost in lives. So it would be a major gift to Moscow and a major sacrifice for Mr. Zelensky, who rejects the idea out of hand.

Some work has been done on what a security guarantee might look like under a “coalition of the willing” led by Prime Minister Keir Starmer of Britain and President Emmanuel Macron of France, with a small headquarters in Paris. Secretary of State Marco Rubio has now been charged with coordination from the American side. But France, Britain and tiny Estonia are the only countries that have indicated that they could deploy troops in a post-settlement Ukraine.

Germany has hesitated and major frontline states like Poland have refused to take part. The Poles, mistrustful of Russia, have said that they want to keep their troops at home for their own defense, and where they are genuinely protected by NATO’s Article 5, rather than vulnerable to incidents or accidents that Russia might use to weaken or divide peacekeepers.

A likely solution could be about 15,000 to 20,000 European troops being deployed in Ukraine, said Camille Grand, a former NATO assistant secretary general who has studied options for such security guarantees. Troops would be away from the front lines, in support of the Ukrainian military, already the largest and most experienced in Europe, with some 900,000 people under arms.

The Europeans would represent a “reassurance force.” Other countries or even the United Nations could provide separate, unarmed frontline observers, aided by satellite and drone surveillance.

The United States would be asked to provide operational intelligence, including satellite cover and information about Russian intentions or troop movements, and perhaps train Ukrainian forces, but without troops on the ground. But “if things go sour,” said Mr. Grand, now an analyst with the European Council on Foreign Relations, “it would be good to have a public commitment that the Americans would not sit on their hands.”

Ideally that would include a vow to use U.S. air power and naval assets.

The Europeans also want to maintain an American troop presence on the eastern flank of NATO, especially if European troops are deployed in Ukraine, potentially weakening NATO’s own deterrence. Europe’s ready forces are relatively small, so a deployment of some of them in Ukraine would shrink NATO’s defense posture.

Ideally, Mr. Grand said, Mr. Rutte and the new NATO and American supreme commander in Europe, Gen. Alexus G. Grynkewich, would be charged with helping the coalition of the willing with planning. NATO is experienced at coordinating different country forces and assets, Mr. Grand said, as it has done in previous non-NATO conflicts, like Libya.

“And none of this needs to be negotiated with Putin,” Mr. Grand said. Russia could be informed but not allowed a veto, he said. He added that Moscow’s reluctance or willingness to accept such guarantees “will be a test of its good faith.”

Still, Mr. Grand said, “what worries me is who in Europe is willing to do something.”

Mr. Starmer has made vague promises but the British military is small, and a commitment to Ukraine is risky and expensive and has no end date. That would normally involve rotational forces with one group in country, one group training to go and one group returning. And it would require materiel support, from arms to barracks, including armor, air defenses, air power and naval power on standby.

Mr. Macron kept his enthusiasm in check after the meeting. Security guarantees come with a peace settlement, and Mr. Putin wants to continue the war, he said. With many details unsettled, it was clear that a deal to end the war is not at hand. “Do I think Putin wants peace? I think the answer is no,” he said. “It’s far from over.”

Johanna Lemola contributed reporting from Helsinki.