There's no shortage of pressing global issues for U.S. President Donald Trump to discuss with the world's most powerful leaders when they gather Friday in Hamburg, Germany, for the G20 summit.

Increasing belligerence from a North Korean regime bent on becoming a nuclear power. Challenges on trade and climate change — both issues where Trump's "America First" doctrine has made the U.S. an outlier.

But there's one encounter that's more anticipated than any other: the meeting between Trump and Russian President Vladimir Putin.

The two will size each other up in what will be the first formal bilateral meeting between American and Russian leaders in nearly two years.

"I expect an Olympian level of macho posturing," said Derek Chollet, an assistant secretary of defence in the Obama administration. "Both have a similar disposition in terms of what they see as strength, as power, what it means to be a man.

"On the substance, I don't expect much."

'Allergic' to the issue

The leaders will likely discuss the war in Syria — a battle in which the U.S. and Russia are at odds over the Kremlin's continued support of Syrian dictator Bashar al-Assad.

Ahead of the meeting, Secretary of State Rex Tillerson said Wednesday the U.S. is willing to work with Russia to create no-fly zones over Syria, for example, setting the stage for that part of the discussion.

Trump and Putin are also expected to talk about the ongoing conflict in Eastern Ukraine, and Putin will likely raise his objection to the U.S. sanctions against Russia over its annexation of Crimea in 2014.

Analyst James Nixey says Trump and Putin's sit-down isn't likely to be a 'meeting of equals,' given Putin's considerable edge in experience. (Dmitri Lovetsky/Pool/Reuters)

But perhaps even more crucial to the political environment back in the U.S. is whether Trump will bring up Russia's meddling in the 2016 presidential election when he sits down with Putin — the man U.S. intelligence officials say ordered the interference campaign to try to help Trump win the White House.

"Putin would deny it," said Thomas Graham, a senior Russia adviser to former president George W. Bush. "But the message that the U.S. is prepared to defend its democratic institutions with whatever means necessary needs to be sent."

But it's a message Trump has yet to show any interest in sending.

The president has tried to dismiss the problem, even as the FBI and Congress investigate not only Russia's hacking and disinformation campaign, but the possibility Trump campaign associates colluded with Russian officials.

At a press conference in Poland Thursday, Trump was asked why he wouldn't unequivocally say it was Russia that interfered in the election.

"I think it was Russia, but I think it was probably other people and or countries ... Nobody really knows, nobody really knows for sure," the U.S. president said.

The consensus from the intelligence community is that Russia was behind the meddling.

"He seems allergic to acknowledging the whole issue even if we take the issue of collusion off the table," said Dana Allin, a senior fellow for U.S. foreign policy at the International Institute for Strategic Studies.

"There's been almost a hysterical denial by the president that this should be something he should take seriously because any word of it tarnishes the beauty of his victory."

But if Trump fails to bring up election meddling with Putin, he risks sending a signal back home that protecting American elections, including next year's midterm votes, isn't a priority.

Trump jokes with Russian Foreign Minister Sergei Lavrov, left, and Ambassador Sergey Kislyak, right, in the Oval Office the day after he fired FBI director James Comey, who was leading the Russia investigation. (Russian Foreign Ministry/EPA)

Still, Allin isn't convinced that consideration will influence Trump's behaviour. Especially, he says, if Trump's behaviour after he fired FBI director James Comey — the man who was leading the investigation into Russian meddling and possible Trump campaign collusion — is any indication.

"This is the president who, the day after he fired James Comey, was yukking it up with the Russian foreign minister in the Oval Office and calling the guy he fired a nut job."

'All eyes are on Trump'

European allies have their own set of concerns and will also be watching Trump closely.

"All eyes are on Trump, not because they're looking for answers," said Chollet, the former Obama adviser. "They're wary."

European leaders like German Chancellor Angela Merkel will be looking for signs Trump is willing to stand up to any future Russian aggression against NATO members. (Jonathan Ernst/Reuters)

Consider what happened during the NATO summit back in May —Trump's first major meeting in Europe. He chastised his European partners for not spending more on defence and he declined to reaffirm the U.S.'s commitment to Article 5, the principle that an attack on one NATO member is an attack on all — a particular concern for NATO partners on the alliance's frontier with Russia.

That Trump eventually did so weeks later during a White House press conference has done little to stifle fears that he won't stand up to Russian aggression.

"Trump is doing a good job of breaking up or undermining the transatlantic alliance which, if the whole situation is zero sum between the West and Moscow, is good for the Russians," Allin said.

'It's not totally a meeting of equals. - James Nixey, Russia program head at Chatham House

The U.S. president indirectly criticized Russia, however, during a joint news conference with Polish President Andrzej Duda on Thursday, when he noted that Poland hosts 5,000 U.S. troops that serve as a deterrent to Moscow's "destabilizing behaviour" in the region.

At the G20 summit, the Europeans will be looking for Trump to avoid taking an overly conciliatory tone with Putin.

Some are concerned about how the two men match up: Putin, the cunning former KGB agent who laments the fall of the Soviet Union, and Donald Trump, an unpredictable novice on the world stage who flouts convention.

"It's not totally a meeting of equals," said James Nixey, head of the Russia program at the Chatham House think-tank in London. "Russia has the upper hand in these negotiations when you consider Trump's experience next to Putin's experience."

Delicate balance

Despite those concerns, it's possible Putin won't see any tangible results from the meeting.

For one thing, Trump has a limited ability to deliver. If, for example, he offered to ease sanctions against Moscow, he would face immense political blowback in the U.S., even from his own party.

The Republican-controlled Senate was so concerned the Trump administration was planning to lift sanctions, it voted almost unanimously last month to give Congress the power to take away the president's ability to do so.

The bill hasn't been passed by the House of Representatives but it shows the strong opposition to Putin.

Trump's meeting with Putin could have significant political consequences back in the U.S. (Jonathan Ernst/Reuters)

The challenge for Trump, according to former Bush adviser Thomas Graham, is to open up the possibility for greater engagement with Russia on the many issues where both countries have a stake — all without seeming too friendly with the Russian leader.

"In order to do that, he has to pay careful attention to the political atmosphere in the U.S. and make sure what's said in public about the meeting doesn't cause a detriment to moving towards broader engagement with Russia," he said.

"Whether the president can do this or not is an open question."