"America and the European Union are best friends", Tusk wrote.
In Helsinki, Putin was asked if he favored Trump in the 2016 presidential election. He is expected to leave the United Kingdom later after staying at his Turnberry resort on Scotland's Ayrshire coast during the private leg of his visit.
Trump set expectations for the summit low, telling CBS News, "I don't expect anything". "I'm not going in with high expectations".
Trump also said that "getting along with Russian Federation is a good thing, not a bad thing".
"It isn't a summit", U.S. Ambassador to Russia Jon Huntsman told NBC'S "Meet the Press". But as to impeachment, we'll see how this plays out.
The Senate Foreign Relations Committee chairman spoke to reporters today who asked for his thoughts on the summit where Trump sided with Putin over USA intelligence conclusions that Russian Federation interfered in the 2016 elections.
Trump says he ran a "clean campaign" and he beat his Democratic presidential rival Hillary Clinton "easily".
The Helsinki summit, which comes at one of the most crucial junctures for the West since the 1991 fall of the Soviet Union, has alarmed some North Atlantic Treaty Organisation allies who fear Putin might seek a grand deal that undermines the USA -led transatlantic alliance.
"Frankly, we have not been getting along for the last number of years".
"You know, I've called it a carve-out for this".
"The US doesn't have and won't have a better ally than the EU".
But the meeting also comes just four days after the Justice Department announced indictments of 12 Russian intelligence agents for a campaign to disrupt the 2016 presidential election.
"The Department of Homeland Security and the Federal Bureau of Investigation, in coordination with global partners, have detected Russian government actors targeting government and businesses in the energy, nuclear, water, aviation and critical manufacturing sectors", Coats said at the Hudson Institute think tank in Washington on Friday.
In a March 1 speech during Putin's reelection campaign, he detailed several new nuclear weapons, each time stressing that U.S. defenses could not handle the new designs.
Ahead of his sit-down with with Mr Putin, who has cracked down on the free press, Mr Trump has continued to unleash a series of attacks on the media, even as Air Force One descended into Helsinki.
As of Friday, the inquiry has indicted 32 people - mostly Russian nationals in absentia - as well as three companies and four former Trump advisers.
The 2018 Russia-United States summit will focus on improving ties between the two countries. I said, make sure that you have a carve-out. "But certainly, I'll be asking about it".
Mr Putin arrived late for the meeting - another display of the Russian's leader famous lack of punctuality. "I think that getting along with Russian Federation is a good thing", Trump told the program.