Coming off a contentious NATO summit and a trip to the U.K. in which he seemed to undercut the government of America's closest ally, President Trump took aim at another Western institution just days before his high-stakes meeting with Russian President Vladimir Putin.

In an interview with "CBS Evening News" anchor Jeff Glor in Scotland on Saturday, President Trump named the European Union -- comprising some of America's oldest allies -- when asked to identify his "biggest foe globally right now."

"Well, I think we have a lot of foes. I think the European Union is a foe, what they do to us in trade. Now, you wouldn't think of the European Union, but they're a foe. Russia is foe in certain respects. China is a foe economically, certainly they are a foe. But that doesn't mean they are bad. It doesn't mean anything. It means that they are competitive," Mr. Trump said at his golf club in Turnberry, Scotland. 

"I respect the leaders of those countries. But, in a trade sense, they've really taken advantage of us and many of those countries are in NATO and they weren't paying their bills," he added.

Trump's Monday morning tweet and his words and actions in the last week have only amplified concerns about his approach to Russia among US allies and lawmakers of both parties in Washington. 

Ahead of his meeting with Putin -- who is alleged to be behind the assassination of journalists and political dissidents -- the US President also lashed out again at the news media on Sunday by branding journalists "the enemy of the people."

Trump again -- as he has repeatedly done -- pointed the finger at his predecessor President Barack Obama and characterized the investigation stemming from Russian election interference as a "witch hunt."

"President Obama thought that Crooked Hillary was going to win the election, so when he was informed by the FBI about Russian Meddling, he said it couldn't happen, was no big deal, & did NOTHING about it," Trump tweeted. "When I won it became a big deal and the Rigged Witch Hunt headed by Strzok!"

Everything from Russian meddling in the 2016 election to the conflicts in Syria and Ukraine are expected to be on the agenda for their summit here in Helsinki.

Trump and Putin arrived separately at the Finnish presidential palace, about 45 minutes behind schedule. Trump held at his hotel while he waited for Putin, who is known for arriving late to important events, to touch down -- drawing comparisons to Trump's late arrivals at recent summits with US allies.