"It's going to be an interesting time in the United Kingdom and an interesting time at NATO", Mr Trump told reporters. In Brussels, they expect Trump to undercut the alliance and demonstrate that the United States is not wholeheartedly committed to it, while they worry that in Helsinki he will sell out the West for the equivalent of a mess of pottage to the master of the Kremlin.
However, allies seem more concerned by Trump's approach than his predecessors'.
But, given a general wariness towards Russian Federation among American voters and Congressional lawmakers, Trump is unlikely to concede too much to Putin, said Michaels.
Trump has, meanwhile, delivered on US commitments to Europe. Trump sent letters to the leaders of several North Atlantic Treaty Organisation countries ahead of his visit, warning that it would become "increasingly hard to justify to American citizens why some countries fail to meet our shared collective security commitments".
Mr Trump told MailOnline: 'He's been very, very nice to me.
Last years' visit to Brussels also produced the famous mano a mano handshake between Trump and French President Emmanuel Macron.
Rep. Eliot L. Engel, a New York Democrat, is ranking member of the US House Committee on Foreign Affairs.
"Mr. Putin represents none of those values", Warner said.
He continued, "suddenly you have a situation where the US president wants to connect the two things".
"We do have a lot of allies, but we can't be taken advantage of", he said. He has often railed against the US's key allies, accusing fueling trade deficits with the US.
Trump has shown little regard for America's traditional bonds with the Old World, publicly upbraiding world leaders at NATO's new headquarters a year ago for not spending enough on defense and delivering searing indictments of Western trading partners last month at an worldwide summit in Canada. This is not fair, nor is it acceptable.
Since Russia's 2014 annexation of Crimea, the country has built up its forces close to Baltic states. Still, Chancellor Angela Merkel, in a weekly podcast on Saturday, said Germany would increase defense spending in its 2019 budget, suggesting Trump's jawboning is paying off. We pay far too much and they pay far too little.
This approach to diplomacy with Russian Federation has foreign policy experts anxious, particularly after Russian Federation still stands accused of meddling with the 2016 USA presidential election and being suspected of carrying out a deadly nerve-agent attack in the UK.