During a rally last week in Montana, Trump vowed that he would "tell NATO: 'You've got to start paying your bills."' The president also bemoaned that Americans were "the schmucks that are paying for the whole thing".
"And we are standing behind them on that", she said.
Trump has shown his affinity for closed-door meetings already during his historic summit with North Korean leader Kim Jong-un last month.
When Donald Trump meets Vladimir Putin, he sits down with a disciplined, detail-oriented and experienced Russian leader who has played on the world stage for more than 18 years, in contrast to the USA president's 18 months in office.
"It's not us", Putin has told Trump, the official summarized.
They will sign off on two new military commands - one to protect Atlantic shipping lanes and one to coordinate troop movements in Europe - as well as a plan to beef up NATO's ability to mobilise forces quickly in the event of a crisis.
British F1 Grand Prix 2018 Results: Sebastian Vettel Wins Dramatic Race
Bottas was fourth with Red Bull's Daniel Ricciardo fifth and Nico Hulkenberg sixth for Renault. Lap 12 - Hamilton is already sixth, as Ferrari's Vettel keeps hold of his lead so far.
"He will have watched the Kim Jong Un summit and he will have the same appraisal: that Trump gave away a major American card without getting anything concrete back for it", said a former senior US official. In addition to plotting global policy together, Putin and Trump have often commiserated with one another over both the "deep state" and "fake news, ' according to one senior official".
"He's mainly anxious about our allies taking advantage of us".
But, given a general wariness towards Russian Federation among American voters and Congressional lawmakers, Trump is unlikely to concede too much to Putin, said Michaels.
And pulling out won't have much support in his administration or among lawmakers.
The U.S. has been seeking an increased commitment by alliance members to increase defense spending. On Putin's wish list: an end to USA military exercises in Europe and the scaling back of US forces there.
"Other countries are going to have to look out for themselves..."
Much, of course, depends on the president's mood, which is rarely good during global conferences where he bristles at what he considers the unfair economic and security alliances the United States constructed in the wake of WWII and the Cold War.