It's been four years since Russia was expelled from the G8 — but the country and its leader will still cast a long shadow over the G7 leaders' summit in Charlevoix, Quebec Friday and Saturday.

Russia's alleged campaign of cyber attacks and interference in foreign elections are matters that at least six of the G7 leaders will want to take up in Quebec.

But the one leader who won't want to dive too deeply into Russia's involvement in Western elections is U.S. President Donald Trump. He's facing daily news headlines about alleged collusion between Russia and his 2016 presidential campaign and is waging a social media war against the special counsel's investigation of Russian interference in that campaign.

Other issues threaten to derail the summit, of course — chief among them trade and tariffs and recent U.S. foreign policy, including Trump's decision to pull out of the Iran nuclear deal. And the off-again, on-again North Korea summit will eclipse the official agenda as well.

But Russia, no longer at the summit table, is set to be a spoiler like no other.

The very large elephant in the room

How do six leaders of the most developed and industrialized economies in the world sit at a table with Donald Trump and talk about alleged Russian interference in elections — when links between Trump's election campaign and Russian interests are the subject of a massive special counsel investigation at home?

"I don't know how they do that. It's going to be awkward," said Meredith Lilly, who was an international trade adviser to former prime minister Stephen Harper and is now a professor with the Norman Patterson School of International Affairs at Carleton University.

"I think it will be very challenging to have an open discussion and a frank dialogue about any issue where there are major trust problems."

Since its expulsion from the group in 2014 over its invasion of Ukraine and annexation of Crimea, Russia has been a dark cloud hanging over the G7.

Even with Trump at the G7 table last year in Taormina, Italy, the leaders were able to reach a consensus on condemning Russian aggression. They'll likely do it again this year.

But following the G7 foreign ministers meeting in April — where the leaders committed to setting up a working group to "call out" Russian "maligned behaviour" — the G7 leaders are looking now at making a similar commitment regarding foreign interference in democratic elections.

There is evidence of Russian attempts to meddle in the recent French and German elections, and in the Brexit referendum that pulled the United Kingdom out of the European Union. With U.S. midterms coming up this fall and Canada's federal election due in 2019, the issue is top of mind for the G7 leaders and their Canadian host.

Alleged Russian online attacks haven't been limited to elections and referenda. In April, the United States and Britain accused Russia of launching cyber attacks on computer routers, firewalls and other equipment used by government agencies, businesses and operators of critical infrastructure around the globe.

The biggest 'wild card'

Russia has denied interfering in the 2016 U.S. presidential election, but special counsel and former FBI chief Robert Mueller is heading a probe that has already ensnared top Trump campaign officials.

Trump, meanwhile, has used public statements and his Twitter account to tar the investigation as "fake news" and a "witch hunt" — which raises doubts about how willing he will be to talk about Russian meddling in elections if he sees the entire topic as an attack on his political legitimacy.

"I think it will be very difficult to have a discussion about Russian issues with Donald Trump," said Laura Dawson, director of the Wilson Center's Canada Institute in Washington D.C.

"Managing the U.S. president is certainly the biggest wild card in this meeting."

And the U.S. president's attitude toward Russia and its president, Vladimir Putin, is — like so many things involving Donald Trump — constantly in flux.

During the 2016 U.S. presidential campaign, Trump praised Putin as a better leader than Barack Obama. Once elected, Trump ordered air strikes against the Russian-backed Syrian regime.

The Trump administration also got on board with sanctions against Russia in March over its alleged election meddling.

'Predictably unpredictable'

But in April, Trump blocked a plan to impose further sanctions on Russia over its support of Syria's chemical weapons attack on civilians.

Trump also defied his own officials' advice and called Putin in March to congratulate him on his landslide win in an election widely seen as a sham.

"He's predictably unpredictable," said John Kirton, director of the G7 Research Group at the Munk School of Global Affairs at the University of Toronto.

Kirton said, however, that on the key issues that got him elected, Trump is fairly consistent.

"We know he hates terrorists, immigrants and multilateral trade agreements," said Kirton, adding that since Trump did not get elected on his Russia policy, he can afford to be changeable.

"And that's the one thing that has changed the most," said Kirton. "(Trump now says) 'I no longer love Putin and the Russians.' So he can flip on that, as he has, without destroying his faith with his base."

And he can flip back again at any time, making an honest conversation about how to push back against Russian election meddling especially 'awkward' and 'difficult' — if not virtually impossible.