Perhaps fearing that Trump's eagerness to forge a bond with Putin be mistaken for cheerful naivety, US officials played along with the serious mood.
Trump and Putin did not shake hands when they entered, sullenly, but only when they began a lengthy closed-door meeting that had the diplomatic world on edge.
And when White House spokeswoman Sarah Sanders tweeted out a picture, she chose a sombre black and white showing Putin's eyes lowered and Trump looking dully angry.
The body langauge was awkward, but television footage later showed Trump offering a stone-faced Putin a reassuring wink.
Perhaps this was to be expected. There is a lot at stake for the presidents, both in terms of global security and their personal and political reputations. But if the occasion stifled their smiles, it was not for lack of a welcome from Helsinki, hosting its biggest East-West summit since the Cold War.
Even the Scandinavian summer was on its best behaviour, with sunshine and 30 degree Celsius heat at the harbour-front venue during almost 20 hours of daylight.
The country has the lowest number of officers per capita of any in the European Union, but the police were able to handle both press and small crowds of peaceful protesters.
A military patrol vessel chugged around the busy harbour from time to time, between cruise liners and tour boats, but there was no theatrical ring of steel. The warm welcome also extended to facilities for the press -- more than 2,000 of whom were accredited to cover the one-day summit.
Both leaders were told "Welcome to the land of free press" by billboards on the route from the airport, paid for by the top-selling newspaper Helsingin Sanomat.
While the White House press corps took over a conference centre overlooking the sun-dappled harbour, international reporters took over the Finlandia Hall.
A venue for classical music designed by celebrated architect Alvar Aalto, the Finlandia was equipped with a lounge to watch Sunday's World Cup final.
Craft beers and local delicacies competed with an on-site sauna to tempt reporters away from their laptops and cameras.
And in 1975, Gerald Ford and Leonid Brezhnev signed the Helsinki Accords, to uphold the post-war carve-up of Europe agreed by Washington, Moscow and London.
So the city has a track record as a bridge between its friends in the West and nearby Russian neighbours -- even if it also has a long memory.
In pride of place among the delicacies on offer to reporters in all the summit venues: Karelian pastries, served with egg butter.
Things have moved on for Finland since their bitter battle for independence. So much so that the 2018 UN World Happiness Report named it the cheeriest spot on Earth.
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)