Over a whirlwind four days of diplomacy designed to end the war in Ukraine, President Donald Trump has met with Russian President Vladimir Putin, Ukrainian President Volodymyr Zelensky, and prominent European leaders.

Trump and Zelensky engaged warmly on Monday, expressing optimism about resolving the now 3 1/2-year war, the bloodiest and largest since World War II. This represents a marked contrast from the two leaders’ disastrous White House meeting in February. Other positive signals have also come to the fore.

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Ukraine and Russia now appear ready to recognize territorial concessions based on the current battlefield front lines. This understanding would entail de facto but not de jure recognition of Russian control over Ukrainian territory in Crimea and southeastern Ukraine. It would also mean Russia tacitly giving up its requirement of total control over the entirety of central-southern and southeastern Ukrainian provinces that the Kremlin falsely claims as Russian territory. While these concessions would be painful for Ukraine, they would be tolerable alongside other evolving elements of the deal.

Notably, there is new confidence that European ground forces could be deployed to Ukraine to provide Kyiv with “security guarantees.” Russia is sending mixed signals here but seems to be insisting that no Western troops enter Ukraine after a peace deal is reach. Still, it is good that Europe is putting meat on the bones of what any security guarantee force would look like. This force would aim to ensure any peace agreement in 2025 is not later smashed apart by a Russian invasion in 2030, 2035, or beyond. Ukraine’s concern is legitimate, given that Russia breached its 1994 Budapest Memorandum treaty obligations via its 2014 seizure of Crimea, and its Minsk 2 treaty commitments via its Feb. 2022 invasion.

What form would a peacekeeping force take?

It would be led by deployments from the United Kingdom, France, and Germany of perhaps 15,000-30,000 troops. This force would act as a so-called “tripwire” deterrence against a future Russian invasion (the tripwire principle was applied during the Cold War in relation to NATO military forces deployed in Berlin to deter an attack by the Soviet Union’s Red Army). Considering the need for the U.S. military to prioritize China-related threats, the burden must fall predominantly on Europe here. In turn, unreliable allies such as Spain and Hungary, which refuse to provide either funding or forces for these efforts, should be expelled from NATO. Similarly, if German Chancellor Fredrich Merz yields to parliamentary pressure not to deploy ground forces to Ukraine, Trump should relocate all U.S. military forces in Germany to other bases in Europe.

The ingredients to make any security guarantees credible are becoming more apparent. One challenge until now has been Trump’s reticence about the possibility of the U.S. military defending European peacekeepers if they were to come under Russian attack. But Trump now says the U.S. will be involved and “will help by air.” While greater detail is needed, Trump’s statement suggests a U.S. air power backstop for Europe. This will be a foundation stone of any successful security guarantee.

As I noted on Monday, “The lack of an American guarantee to come to the aid of allies that might be attacked in the future poses two key challenges. First, it will fundamentally damage Ukraine’s confidence that any security guarantees are worth the paper they are written on. If Nigel Farage becomes the next U.K. prime minister and Jordan Bardella the next French president, for example, troops from those countries might quickly be withdrawn from Ukraine. Putin can then return to conquest, rearmed and resupplied by years of post-sanctions peace. Only America has the strategic credibility to be reliable here. The Europeans also know that the Russians know this, which is why they are so determined to ensure any security guarantees have teeth. Trump can get the Europeans to pay for any security guardrails and man its de facto ramparts, but America will have to be ready to step in if the Russians decide to restart any conflict.”

Other complicated considerations remain, however.

For a start, Zelensky and Putin have yet to meet. On Monday, Trump again pushed for the two leaders to meet, followed by a trilateral meeting involving himself. But while Zelensky has expressed openness to an immediate bilateral engagement with Putin, the Russian leader seems to be playing games.

Responding to Trump’s entreaty on Monday, Putin suggested Zelensky come to Moscow. This was a very direct insult to Zelensky and, frankly, to Trump. It shows Putin’s desire to broadcast his overarching belief that Ukraine belongs to Russia, and his interest in signaling dominance over Zelensky (Trump is beginning to recognize how to turn this gamesmanship back against Putin). Russian foreign minister Sergey Lavrov is also playing down a near-term timetable for any meeting. This further indicates that Putin is playing for time, doing only the absolute minimum to avoid devastating new U.S. sanctions. In response, Trump should give Putin a deadline of seven days to meet with Zelensky or suffer those sanctions.

Other questions also need resolution.

Take Ukraine’s demand that Russia pay significant reparations for the immense damage that it has caused since February 2022. Putin will be reticent to agree to compensation payments for reasons of both pride and practicality. Russia’s economy is struggling, and its government revenues are running low. A possible solution may be found by providing Ukraine with access to Russian assets seized since the war began.

Similarly, international sanctions relief for Russia must be tempered to incentivize Russia’s acceptance of a peace agreement and its post-signing compliance. The conduct of the Russian intelligence services inside Ukraine will be particularly important in this regard.

After all, where Putin has previously decided that direct military invasion of a perceived hostile country is impractical, he has repeatedly deployed covert intelligence officers to spread discord, murder, and even pursue attempted coup d’etats. A good example here comes from the Russian GRU military intelligence service’s failed 2016 coup attempt in Montenegro. Any viable peace deal will thus require so-called “snap back sanctions” or similar measures to impose timely, direct costs on any Russian undermining of Ukraine’s stability or sovereignty.

Another issue?

U.S.-Russia relations following any peace agreement. While U.S.-European trade/investment is vastly more lucrative to the U.S. than any credible prospect of even much increased U.S.-Russia trade/investment, Trump is excited by the prospect of new U.S.-Russia economic cooperation. While this is not concerning in and of itself, the Kremlin will attempt to exploit any such cooperation to earn American political latitude to increase its hostile intelligence and military activity against Europe. Moreover, American business executives wishing to deal in Russia should be wary that while their new Russian engagements might make a quick buck, they will also bear significant medium-longer term risk of Justice Department corruption charges or their flying out of high-story windows.

In the same way, any new U.S.-Russia nuclear agreements must carry safeguards to ensure that Russia does not break its word. As with the Chemical Weapons Convention, the Intermediate-range nuclear forces treaty, and the Outer Space Treaty, Putin is happy to sign arms control treaties and then systematically break them.

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Where does this leave us?

Momentum towards peace is clearly growing in Trump, Europe, and Ukraine. This is a good thing. But until Putin defers his penchant for KGB deception in favor of more constructive actions, it will be hard to find cause for real optimism.