Hours before leaving for a gathering with his Nato allies in Brussels, Trump commented that it might be "easier" meeting with his Russian counterpart Vladimir Putin instead.
The US president has made no secret of his misgivings about the 29-member alliance that he considers too expensive for US tax payers.
"Truth be told, America does foot the majority of Nato spending," recognises Mitchell Belfer, Director of the Euro-Gulf Information Centre in Rome.
Yet it also benefits from the alliance, he insists. "The United States benefits much more than its European allies do by being able to base itself along the frontiers of its former adversary Russia and, previously, the Soviet Union," he told RFI.
"America no longer views Europe as being a security provider in its own right or even assisting America generate its strategic position and that’s a problem."
It underscores the growing rift between the US and Europe, deepened by recent steel tariffs introduced by Washington, triggering retaliatory measures from the European Union.
"Trump does not get on well with his allies," comments Ulrike Esther Franke, a policy fellow at the European Council of Foreign Relations in London.
"It's not just Nato, the G7 was the same situation. The G7 that was called G6+1 or G6 versus 1 just because it was so adversarial. So I'm not really surprised that he expects to have a better meeting with Vladimir Putin, although this is absolutely absurd," she told RFI.
Is Nato obsolete?
The military alliance was founded in 1949 to counter the influence of the Soviet Uniion during the Cold War.
That threat no longer exists, according to Yves Boyer, Director of the Foundation for Strategic Research in Paris, suggesting Nato may be obsolete, as Trump has previously claimed.
"There is no pressing need to maintain Nato as a guardian against the so-called Russian threat. It’s not a threat. Russia has a GNP the size of Spain, it has good armed forces but no political incentives for the Kremlin to launch an attack on Europe," Boyer told RFI.
Belfer, however, disagrees.
"If Russian behavior in Ukraine or Georgia is anything to go by, given the opportunity Russia would roll back into central and eastern Europe and that is something that should be prevented," he argues, saying Nato remains a "bulwark against any kind of intervention of Russia into the Baltic states".
Trump visits Moscow
For Boyer's part, he doesn't call for the alliance to be scrapped but to be reformed.
"It means building for the 21st century a new kind of military relationship with the US on the one hand and on the other to cope with new threats from the south, the Mediterranean or elsewhere," he says. "We have to be imaginative, innovative and not stick to the past.”
Yet Nato member states are struggling to deal with the present, notably their relations with Russia.
And the fact that Trump is catering to Putin - he heads to Helsinki after the Brussels summit for direct talks with the Russian president - doesn't help, reckons Ulrike Franke.
“If the US doesn't have a clear stance or becomes too cosy with Russia this all becomes very confusing", she told RFI. "It becomes very difficult on how to confront or even have a common clear policy with regards to this country that, although it may not be a direct military threat, is a political threat that the alliance has to deal with."
Nato will also have to deal with the highly unpredictable US leader because whatever Trump says or does could be decisive for its future.