President Donald Trump, right, and Russia President Vladimir Putin talk during the family photo session at the APEC Summit in Danang in 2017. File picture: Mikhail Klimentyev/Sputnik

After an unconventional courtship that began before his presidential run, US President Donald Trump and his Russian counterpart, Vladimir Putin, will come together in Helsinki. Western allies are on edge amid speculation Trump may recognize Russia's annexation of Crimea.

Washington/Moscow - After doing all he can to rattle and alarm the US' traditional allies in Europe by imposing tariffs on their exports and threatening the NATO security umbrella, President Trump is set to meet his Russian counterpart Vladimir Putin in Helsinki.

"The fact that this is the first major summit between Trump and Putin is significant given how Trump has repeatedly expressed desire to improve relations with Russia," says Erik Brattberg, the director of the Europe Program at the Carnegie Endowment for International Peace.

Trump brushed off concerns about his attempt to get closer to Moscow at a Montana rally last week, just days before heading to Europe - first to a NATO summit in Brussels and later to Helsinki.

"Getting along with Russia and getting along with China and getting along with other countries is a good thing, it's not a bad thing," he told cheering supporters.

Blaise Misztal of the Bipartisan Policy Center said the meeting in Belgium could set the tone for the July 16 summit, adding that "Putin is likely to want to play on and expand any cracks in the unity of the alliance that emerge from the NATO summit."

Looming over Helsinki meeting are allegations that Russia meddled in the 2016 US presidential elections in favour of Trump. A recent bipartisan report by the US Senate backed this assessment, which also enjoys consensus in the US intelligence community.

But Trump is unlikely to seriously raise the issue in Helsinki, says Brattberg, noting that the US president "has previously rejected claims of Russian meddling and said that he trusts Putin's word on the issue."

Trump's critics take issue with the fact that he has chosen to go easy on Russia while sparring with Canada, France and other allies. Trump frames these traditional allies as countries that cost the US money, whether on trade or providing them protection.

Daniel Fried, a former US ambassador to NATO, explains the shift in the US as a re-emergence of a long-suppressed national tendency towards isolationism.

"That American tradition is back, for the first time in 80 years, and Trump has tapped into it," says Fried, who now works at the Atlantic Council think tank.

Russian political and security expert Nabi Abdullaev warns that Helsinki may yield little in the way of concrete policy outcomes.

"The two leaders will get their share of flashy PR gains for their respective domestic audiences," Abdullaev said.

Ukraine and Syria are likely to feature prominently during the talks.

Trump wants to wind down in Syria and pull out US troops. Putin is the main power broker in the war-torn country. If he can offer Trump help, the US president might jump on the chance.

However, Abdullaev warns that Russia is not in a position to push Iran out of Syria, a key demand of Israel, with whom Trump remains close.

"Russia's leverage over Iran is not strong enough to override Syria's strategic importance to Iran," Abdullaev said.

Whatever assistance Putin may offer on Syria could be matched with a US gesture on Ukraine, after Trump's refusal to rule out US recognition of Russia's 2014 annexation of the Crimea region from Kiev.

This would mean allowing Europe's borders to be changed through the use of force. Any wedge in Europe - including the recent drift of Turkey towards Moscow - is seen as a win for Russia.

Trump does not control everything and he cannot offer endless concessions. For example, the sanctions on Russia over Ukraine come from Congress. Also, even though Trump talks of potentially winding down in Europe, in reality the US is expanding its military presence.

Misztal of the Bipartisan Policy Center said Putin "may seek to dissuade President Trump from any greater defence cooperation with Poland or the Baltic," as Russia still remains wary of US interests in the region.

Fried had some advice for Trump before he sits down with Putin one-on-one with only interpreters in the room.

"Don't give away anything for nothing. Don't do dumb deals. There is nothing wrong with working together with the Russians, but don't pay extra for the privilege," he said. "Remember who your friends are."