“I have NATO. I have the U.K., which is in somewhat turmoil. And I have Putin,” Donald Trump explained to reporters Tuesday on the White House lawn, laying out his itinerary before departing for Europe. “Frankly,” he predicted, before boarding his helicopter, “Putin may be the easiest of them all.” Those parting thoughts have turned out to be prescient: the United Kingdom is indeed in turmoil after Trump, having bashed NATO in Brussels, promptly ignited another diplomatic and political crisis in London. The diplomatic community had been hoping against hope that Trump might bolster the international alliance before jetting off for his alone time with the Russian president in Helsinki, to no avail. “What would be really great would be to have the allies united, strong, showcasing resolve with a big sense of purpose,” sighed Julianne Smith, a NATO vet who served as Joe Biden’s deputy national security adviser. Instead, she told me, “what we’re gonna have before he goes to meet Putin is a divided alliance, a contentious meeting, anger and frustration on all sides . . . for Putin, this is a real win.”

The more pressing fear, however, is what Trump will say or do when he and Putin meet on Monday, face-to-face. As The New Yorker’s Susan Glasser reports, preparations for the Helsinki summit have been unusually limited, prefaced only by National Security Adviser John Bolton’s single trip to Moscow last month. Even more alarming to foreign-policy experts, there is still no formal agenda for the meeting. Ordinarily, diplomats and aides would have established a list of “deliverables” ahead of such a high-profile event—especially one in which Trump is planning to first meet with Putin alone. Instead, according to Glasser, the Russians told Bolton, “The meeting is the deliverable.” Asked about their sit-down on Thursday, Trump signaled that his conversation with Putin would be unscripted, characterizing it as a “loose meeting.”

This, as a former senior State Department official told me last month, is the worst-case scenario for the Trump-Putin summit. “My concerns on such a summit revolve around the agenda. . . . While the ‘surprise’ value of starting with a Trump-Kim summit might have worked in the D.P.R.K. case, it won’t with the Russians,” this person said, referring to Trump’s June 12 meeting with North Korean dictator Kim Jong Un. “I’d want to see plenty of meetings—both internal U.S. and with Russian counterparts—at lower levels to talk through the whole range of issues with the Russians . . . But I worry that the style of this president may push toward a meeting that isn’t fully fleshed out. And, to my mind, that plays to Russia’s advantage.”

Trump, however, has apparently dismissed all efforts to constrain his dialogue with Putin, viewing their meeting as long overdue. “He thinks that they are two strongmen-minded leaders,” said a source familiar with previous administrations’ attempts to open a conversation with Putin. “He thinks that together they will be able to get through the clutter of the ‘deep state’ as he calls it and actually get things done.” Already, Trump has U.S. allies concerned. During his impromptu news conference on Thursday, the president didn’t rule out agreeing to cease NATO military exercises in the Baltics, or recognizing Crimea as part of Russia. “People like to say, ‘Oh Crimea,’ but the fact is they built bridges to Crimea, they built, I think, a submarine port,” Trump said. “What will happen with Crimea from this point, that I cannot tell you. But I am not happy about Crimea, but again that was Barack Obama’s watch, not Trump’s watch.”

At the core of these worries lies a more specific fear: what concessions might the former K.G.B. operative extract from Trump when the two are alone together, without aides, or even a blueprint to guide their conversation? In lieu of a public agenda, diplomats have been forced to read the tea leaves to divine what the two leaders might discuss. Potential topics range from nuclear disarmament to Russia’s 2014 annexation of the Crimean peninsula to the ongoing war in Syria, and certainly to Russian interference in the 2016 election. That the Trump-Putin summit is in Helsinki is not without historical significance. Back in 1975, another summit was held in the Finnish city that proved to be one of the most consequential episodes of the Cold War. Under the leadership of Gerald Ford, the U.S. signed the Helsinki Accords with the Soviet Union and nearly all of Europe, setting forth a code of international conduct that included protecting human rights. Arguably, there could be no more fitting backdrop for Trump to condemn Russian interference in U.S. elections, along with the rampant human-rights abuses that have occurred on Putin’s watch.

But few expect that much. On Friday, just hours before Robert Mueller indicted a dozen Russian intelligence officers for allegedly hacking the D.N.C. and Clinton campaign, Trump offered only a half-hearted response when asked whether he would press Putin about Russia’s meddling in the 2016 election. Trump insisted that he “will absolutely, firmly ask” about Russia’s meddling in the 2016 election, but hardly seemed convinced, himself. As recently as two weeks ago, he questioned whether Russia had interfered in the election at all. Instead, diplomats seem mostly resigned to the probability that Trump will fall for Putin’s flattery and leave the summit as he did his meeting with Kim: with nothing but praise for an authoritarian. According to one Senate aide I spoke with, the lowest bar Trump could clear would be, “Will he just avoid a complete crisis?”