President Donald Trump has finally found a way to like arming Ukraine: ask European allies to donate their weapons, and sell them American replacements.

Now comes the hard part — agreeing on who will actually give up their prized systems, including the Patriot missile batteries that Kyiv has been desperately seeking. "We're going to make top-of-the-line weapons, and they'll be sent to NATO," Trump said in the Oval Office on Monday.

Some Patriot missile defense systems should arrive in Ukraine "within days," added Trump, who faces resistance from some high-profile figures in the MAGA movement who oppose U.S. support for Ukraine.

The costly Patriot systems - in high demand among U.S. allies - have proven effective at destroying Russian ballistic missiles aimed at Ukraine's cities.

The U.S. has also signaled willingness under the proposed arrangement with European allies to send additional offensive weapons, said one source familiar with the matter, though Trump has said that Ukraine should refrain from attacking Moscow.

The plan, which Trump and NATO Secretary General Mark Rutte hatched in recent days, according to two sources familiar with the discussions, has been received positively by Ukraine and its allies.

Leaders in Kyiv and elsewhere have celebrated a major tonal shift from Trump, who had until recent weeks spoken glowingly of Russian President Vladimir Putin.

But since the announcement, it has become clear Trump presented a framework - not a fleshed-out plan. How material any support ends up being for Ukraine will depend on coming negotiations about who provides which equipment, according to 10 officials in the U.S. and Europe.

"As always with these things, the devil is in the details," said one northern European ambassador in Washington.

The central question is who would donate the Patriot batteries, and when.

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During his Oval Office meeting with Trump on Monday, Rutte mentioned six NATO countries - Finland, Denmark, Sweden, Norway, the Netherlands and Canada - that were willing to participate in the weapons-purchasing scheme.

High-ranking sources at two of those countries' embassies in the U.S. told Reuters they personally learned of the plan as it was announced. Even close U.S. allies appeared to learn of the proposal in real time.

"It is my clear sense that nobody has been briefed about the exact details in advance, and I also suspect that internally in the administration they are only now beginning to sort out what it means in practice," said a separate European ambassador.

Kurt Volker, a former U.S. ambassador to NATO, said Trump found a way to balance support for Ukraine with the political realities of the Republican Party. Having the European allies underwrite U.S. arms supplies is "very consistent with what he (Trump) said during the campaign," he said. Throughout the campaign, Trump said he would push European countries to spend more on defense, to great applause from MAGA crowds. "You gotta pay," he said. "If they're not going to pay, we're not going to protect, ok?"

Volker said Ukraine could ultimately receive 12 to 13 Patriot batteries but it could take a year for them all to be delivered.

Asked for comment, a NATO official said the defense alliance would coordinate weapons deliveries through a mechanism known as the NATO Security Assistance and Training for Ukraine, a NATO mission located in Germany that is responsible for coordinating Western military aid for Kyiv.

"Several European countries have already committed to support this initiative including Germany, Norway, Denmark, the Netherlands, Sweden, the United Kingdom, Canada and Finland," the official said. "Details are still under discussion."

In response to a request for comment, the Pentagon referred Reuters to Trump's Monday remarks announcing his agreement with Rutte.

The White House did not respond to a request for comment, nor did the Ukrainian or Russian embassies in Washington.

'WE ARE READY' The rapid hardening of Trump's rhetoric toward Moscow in recent weeks has come amid an increasingly firm belief that Putin is not engaging in good-faith negotiations, according to two U.S. officials.

"At a certain point, you know, ultimately talk doesn't talk. It's got to be action. It's got to be results," Trump said during his meeting with Rutte on Monday. One of the officials said Trump came to realize that Putin's ambitions extend beyond Crimea and four eastern regions of Ukraine, a point Kyiv and European allies have publicly and frequently made. Three Russian sources close to the Kremlin said Putin will not stop the war under pressure from the West and believe that Russia - which has survived the toughest sanctions imposed by the West - can endure further economic hardship, including Trump's Monday threat to impose U.S. tariffs targeting buyers of Russian oil.

Now, three U.S. officials involved in weapons matters said, the real work begins.

U.S. officials are now talking with NATO allies and gauging who is willing to send what to Ukraine. European officials have been broadly receptive.

"We are ready to participate," Danish Foreign Minister Lars Lokke Rasmussen told reporters in Brussels on Tuesday ahead of a meeting of European Union ministers.

One official cited Germany, Greece, the Netherlands and Spain as good candidates to send a Patriot battery to Kyiv, either because they had multiple batteries or the threats they face are relatively remote.

Some, including Greece and Spain, have previously resisted appeals from allies to give some of their Patriot systems to Ukraine, arguing that they are essential to defend their own countries and NATO as a whole.

Trump's move to take credit for the additional weapons headed to Ukraine has created some mild friction in Europe.

"If we pay for these weapons, it's our support," said EU foreign policy chief Kaja Kallas, speaking after the Brussels meeting, adding that she welcomed Trump's decision.

"So it's European support, and we are doing as much as we can to help Ukraine ... If you promise to give the weapons, but say that somebody else is going to pay for it, it's not really given by you, is it?"

One of the officials said that the Trump administration has been going through NATO inventories to see what's available. Their next effort is to attempt to persuade the allies to gift the equipment to Ukraine in exchange for a "trade" of some sort, the official said.

The trade could be a variety of things, the official said, including giving up an impending acceptance of a piece of military equipment through the Foreign Military Sales program, or sending munitions to Ukraine in exchange for an earlier replenishment date.

Trump told reporters there was one country with 17 Patriots, some of which would go directly to Ukraine. The figure has caused widespread confusion among European allies and on Capitol Hill - many of whom have not been briefed - according to the U.S. and European officials.

No NATO member except the U.S. has that number of Patriot systems, said two sources familiar with the matter, causing speculation that Trump may have been referring to particular Patriot components, like launchers or missiles. German Defense Minister Boris Pistorius, who visited the Pentagon on Monday, said the Germans would discuss sending Patriot batteries to Ukraine with the U.S. in the coming days or weeks. But no Patriot system would arrive in Kyiv for months, he said, likely delaying any receipt until after the tactically crucial summer months.

Another official said Trump was engaged directly in negotiations, though talks so far were "squishy."

"So far folks have said, 'We can help,'" that official said.

"Now, what that means, we don't know."